When I opened up the case he remarked to me, "Why do you have unbuffered DDR400 with a FX-55?" "You should have registered DDR400 with that CPU."
Your friend doesn't know what the hell he's talking about. You use registered ECC memory with socket 940 motherboards and processors which are server boards........the FX originally was a server based processor on 940, but on 939 it's a good ole fashion monster desktop processor.
Registered ECC RAM is slower because that ECC stands for Error Correction Control I believe. Fixes errors within itself, that's why it's slower.
You need unbuffered so you are fine, and he is dumb
So slap him a good one.
EDIT: To clarify like I said, the FX original purpose was infact a server chip that's why AMD site will say use registered