If you are using 5.00 M33-6 or 6.39 ME-4, try to enable the Memory Stick Access speedup for at least GAME mode.
Originally Posted by samagon
If you are using any other M33, GEN or neur0n's firmwares before 6.39 ME-4, you can't really do anything to the firmware except for installing the old 5.00 M33 FATMSMOD patch (But this has some side effects).
Blame Sony for replacing the Memory Stick driver with a really slow one since the days of FW 3.80 to around FW 6.00.
Above all, do not compress games unless your memory stick can be accessed quickly.
Compression does slow down performance dramatically.
Unmodified SCPH-77006 with SM 3.6
SCPH-39006 with M-chip modchip, SCPH-10281 NA and refurb Seagate 80GB HDD
SCPH-10000 v1.00 with SCPH-10190 PCMCIA NA and SCPH-20400 HDD unit