Ok, I'm the first with my results. I think the fsb-wall come only from the cpu's and the AOPEN i975Xa-YDG is not the reason ...
CPU ：Intel Core Duo T2500
M/B ：AOPEN i975Xa-YDG
MEM ：2GB Crucial Ballistix PC6400
HDD ：Samsung S-ATAII 200gb
VGA ：6800GTO @ Quadro 34000
POWER: Cooltek Realplug 600W (4x12V)
CPU COOLER：XP90C / Yateloon SL 90mm (silent 5V)
OS ：WIN XP SP2