I've gone through my log for downgrading a PS3 from 3.5FW to 3.41FW. It looks like there might be useful information in there, so I figured I'd post it up here for someone who actually knows something about the PS3 (so not me) to take a look at. I'm hoping it might be useful in some small way.

manufacturing updating start

PackageName = /dev_usb000/PS3UPDAT.PUP

settle polling interval success
vflash is disabled...
boot from nand flash...
creating flash regions...
create storage region: (region id = 2)
format partition: (region_id = 2, CELL_FS_IOS:BUILTIN_FLSH1, CELL_FS_FAT)
create storage region: (region id = 3)
format partition: (region_id = 3, CELL_FS_IOS:BUILTIN_FLSH2, CELL_FS_FAT)
create storage region: (region id = 4)
format partition: (region_id = 4, CELL_FS_IOS:BUILTIN_FLSH3, CELL_FS_FAT)
create storage region: (region id = 5)
create storage region: (region id = 6)

Initializing
taking a while...
start Updating Proccess
Initialize elapsed time = 100 msec

check UPL
Check UPL elapsed time = 52 msec

check Package Size
get package size elapsed time = 8 msec

start Updating Package
Update packages num = 30
Update packages total size = 162260220

Update Package Revoke list
read package revoke list package (576 bytes) elapsed = 23 msec
update package revoke list elapsed = 107 msec
Update Package Revoke list done(0x8002f000)

Update Core OS Package
read core os package (5182047 bytes) elapsed = 268 msec
update core os package elapsed = 1692 msec
Update Core OS Package done(0x8002f000)

Update VSH Package
sys_memory_container_create() success(id = 0xc0effffe)

Update VSH's package : 1/22
read vsh package (1847 bytes) elapsed = 8 msec
decrypt and verify vsh package elapsed = 29 msec
write vsh package elapsed = 7719 msec
compare vsh package elapsed = 1 msec

Update VSH's package : 2/22
read vsh package (4779244 bytes) elapsed = 248 msec
decrypt and verify vsh package elapsed = 303 msec
write vsh package elapsed = 2712 msec
compare vsh package elapsed = 390 msec

Update VSH's package : 3/22
read vsh package (1927089 bytes) elapsed = 105 msec
decrypt and verify vsh package elapsed = 128 msec
write vsh package elapsed = 674 msec
compare vsh package elapsed = 145 msec

Update VSH's package : 4/22
read vsh package (5498561 bytes) elapsed = 283 msec
decrypt and verify vsh package elapsed = 343 msec
write vsh package elapsed = 3323 msec
compare vsh package elapsed = 445 msec

Update VSH's package : 5/22
read vsh package (2010269 bytes) elapsed = 111 msec
decrypt and verify vsh package elapsed = 134 msec
write vsh package elapsed = 1014 msec
compare vsh package elapsed = 166 msec

Update VSH's package : 6/22
read vsh package (25242 bytes) elapsed = 11 msec
decrypt and verify vsh package elapsed = 29 msec
write vsh package elapsed = 1406 msec
compare vsh package elapsed = 9 msec

Update VSH's package : 7/22
read vsh package (7663270 bytes) elapsed = 396 msec
decrypt and verify vsh package elapsed = 391 msec
write vsh package elapsed = 14767 msec
compare vsh package elapsed = 474 msec

Update VSH's package : 8/22
read vsh package (10258879 bytes) elapsed = 531 msec
decrypt and verify vsh package elapsed = 284 msec
write vsh package elapsed = 15746 msec
compare vsh package elapsed = 529 msec

Update VSH's package : 9/22
read vsh package (8773195 bytes) elapsed = 449 msec
decrypt and verify vsh package elapsed = 241 msec
write vsh package elapsed = 6830 msec
compare vsh package elapsed = 410 msec

Update VSH's package : 10/22
read vsh package (8827678 bytes) elapsed = 458 msec
decrypt and verify vsh package elapsed = 320 msec
write vsh package elapsed = 10991 msec
compare vsh package elapsed = 500 msec

Update VSH's package : 11/22
read vsh package (6182668 bytes) elapsed = 325 msec
decrypt and verify vsh package elapsed = 204 msec
write vsh package elapsed = 2116 msec
compare vsh package elapsed = 351 msec

Update VSH's package : 12/22
read vsh package (10251215 bytes) elapsed = 535 msec
decrypt and verify vsh package elapsed = 255 msec
write vsh package elapsed = 3889 msec
compare vsh package elapsed = 466 msec

Update VSH's package : 13/22
read vsh package (10187344 bytes) elapsed = 522 msec
decrypt and verify vsh package elapsed = 260 msec
write vsh package elapsed = 5959 msec
compare vsh package elapsed = 472 msec

Update VSH's package : 14/22
read vsh package (10381187 bytes) elapsed = 547 msec
decrypt and verify vsh package elapsed = 260 msec
write vsh package elapsed = 5779 msec
compare vsh package elapsed = 482 msec

Update VSH's package : 15/22
read vsh package (9899962 bytes) elapsed = 511 msec
decrypt and verify vsh package elapsed = 259 msec
write vsh package elapsed = 7026 msec
compare vsh package elapsed = 470 msec

Update VSH's package : 16/22
read vsh package (8210627 bytes) elapsed = 433 msec
decrypt and verify vsh package elapsed = 204 msec
write vsh package elapsed = 5004 msec
compare vsh package elapsed = 390 msec

Update VSH's package : 17/22
read vsh package (10382360 bytes) elapsed = 568 msec
decrypt and verify vsh package elapsed = 264 msec
write vsh package elapsed = 6637 msec
compare vsh package elapsed = 560 msec

Update VSH's package : 18/22
read vsh package (9649989 bytes) elapsed = 506 msec
decrypt and verify vsh package elapsed = 369 msec
write vsh package elapsed = 34246 msec
compare vsh package elapsed = 859 msec

Update VSH's package : 19/22
read vsh package (7751745 bytes) elapsed = 407 msec
decrypt and verify vsh package elapsed = 351 msec
write vsh package elapsed = 25385 msec
compare vsh package elapsed = 765 msec

Update VSH's package : 20/22
read vsh package (8165430 bytes) elapsed = 432 msec
decrypt and verify vsh package elapsed = 367 msec
write vsh package elapsed = 12510 msec
compare vsh package elapsed = 702 msec

Update VSH's package : 21/22
read vsh package (8287111 bytes) elapsed = 440 msec
decrypt and verify vsh package elapsed = 349 msec
write vsh package elapsed = 20491 msec
compare vsh package elapsed = 761 msec

Update VSH's package : 22/22
read vsh package (5315230 bytes) elapsed = 291 msec
decrypt and verify vsh package elapsed = 224 msec
write vsh package elapsed = 1818 msec
compare vsh package elapsed = 374 msec

Update VSH Package done(0x8002f000)

Bul-ray Disc Player Revoke
read bdp revoke package (1905 bytes) elapsed = 24 msec
decrypt and verify bdp revoke package elapsed = 31 msec
write bdp revoke package elapsed = 2362 msec
compare bdprevoke package elapsed = 59 msec
Bul-ray Disc Player Revoke done(0x8002f000)

Update Program Revoke list
read program revoke list package (736 bytes) elapsed = 24 msec
update program revoke list elapsed = 308 msec
Update Program Revoke list done(0x8002f000)

move_2block_status_into_the_region(): region id = 3
rewrite_region() region id = 0x3, start_lba = 0x0, end_lba = 0x4000
rewrite region done (ret = 0x8002f000)
rewrite region elapsed time = 1016 msec
touch_1st_sector_in_block() region id = 0x3, start_lba = 0x0, end_lba = 0x4000
touch_1st_sector() done (ret = 0x8002f000)
touch_1st_sector() elapsed time = 1309 msec
rewrite_region() region id = 0x3, start_lba = 0x0, end_lba = 0x4000
rewrite region done (ret = 0x8002f000)
rewrite region elapsed time = 1017 msec

Update BD firmware
read BD firmware package (1966992 bytes) elapsed = 106 msec
update BD firmware elapsed = 188 msec
read BD firmware package (951040 bytes) elapsed = 53 msec
update BD firmware elapsed = 145 msec
read BD firmware package (951040 bytes) elapsed = 55 msec
update BD firmware elapsed = 143 msec
read BD firmware package (951040 bytes) elapsed = 54 msec
update BD firmware elapsed = 144 msec
read BD firmware package (1639296 bytes) elapsed = 89 msec
update BD firmware elapsed = 153 msec
read BD firmware package (787200 bytes) elapsed = 46 msec
update BD firmware elapsed = 144 msec
read BD firmware package (1639296 bytes) elapsed = 89 msec
update BD firmware elapsed = 155 msec
Update BD firmware done(0x8002f000)

Update Multi-Card controller firmware
read MCC package (28636 bytes) elapsed = 25 msec
update MCC elapsed = 28 msec
Update Multi-Card controller firmware done(0x8002f000)

Update BlueTooth firmware
read BT package (644322 bytes) elapsed = 38 msec
update BT elapsed = 58 msec
Update BlueTooth firmware done(0x8002f000)

Update System controller firmware
read SC patch package (4864 bytes) elapsed = 22 msec
read SC patch package (4864 bytes) elapsed = 23 msec
read SC patch package (4864 bytes) elapsed = 23 msec
Update System controller firmware done(0x8002f000)

update package elapsed time = 234840 msec
post processiong...
post processiong done

cleanup update status (ret = 0)
os version = 03.4100
build_version = 45039,20100721
region of core os package = 0x40000000
build_target = CEX-ww
build target id = 0x83
manufacturing updating SUCCESS(0x8002f000)
set product mode (ret = 0)
Total Elapsed time = 237272 msec
This came from a CECHG03 PS3... so UK model, no B/C and therefore no large NAND chips.