Fully Buffered RAM

hey everyone i've finally got the chance to get a new pc and found 2 that caught my eye.
one is a xeon 5130 @ 2.66Ghz with 4gb of fully buffered ram and the other was custom built by me but had a c2d e6600 and only 2Gb of unbuffered ram. either way which ever i get i've got an 8800GTX to put in.

my question is, whats fully buffered ram like compared to unbuffered ram when gaming? and what are xeons like compared to there core 2 duos equivilant? i'm not bothered about price of xeons and stuff i'm just intrested in performance here

thanks