Short answer, ftp. The ps3 has a gigabit network adapter that's 1000mb/s. Usb 2.0 has a max speed of 480mb/s. (Both are theoretical speeds)
Connect the ps3 with a cat6 cable to a gigabit network with a cat6 cable to a gigabit network adapter on a pc (or directly to the pc, and manually assign ip addresses), and it'll be faster. I may have my notation wrong there, but meh.
1000/8 = 125 Megabytes/s
480/8= 60 Megabytes/s.
For you, some basic math answers that question. (Assuming your numbers are correct)
Therefore, ftp is faster.
STOP! Before you ask questions... READ the first post! RTFFP = Read The F*cking First Post
Yes, A 3.55 "jb" (cfw) is available, no >3.55 "jb" or cfw yet.
Yes, A 3.55 downgrade is available. But not to lower than stock firmware! (What it came with)
No >3.55 downgrade is out there yet.