I am suffering from the same problem. I purchased a PS3 Key unaware of the fact it will not jailbreak my system running 3.55. It seems as if I am just screwed unless I return the system and try to find another 320 GB console that hasn't been upgraded to 3.5 yet.
My (most likely painfully nieve and novice) inquiry is "Will Restoring your PS3 result in the downgrade of the system version back to the version it came with out-of-box?" I already seriously doubt it. If not, what can be done to take my firmware version from 3.55 back to 3.41 so that I can use the PS3 Key I recently purchased. Any help will be greatly appreciated.