Im using a Asus P5B Deluxe, which I can take up to about 505FSB. When I was deciding, it was between the P5B and the Gigabyte DS4, but I decided on the P5B in the end as it has less complicated heatpipe cooling(Doesn't attach to the SB) which was usefull as ive watercooled the NB.
Edit; Mines a Gray Mole build as well.
Edit Edit;
Are you sure you can only get 400FSB? You sure its not just the FSB strap "Blackhole" your hitting? I think its between 360fsb-400fsb, things really get stressed, but as soon as you go over that, things ease off again right up to 500 or so. If I was you I'd try and see if you can boot at something like 420-450fsb.