The reviews for that board seemed to indicate that it ran fine at KT400. I believe it still had the restrive of only one stick of RAM if one wishes to run at KT400.
I have two 512MB Corsair XMS PC3200C2 DIMMS for my Asus A7V8X (Also KT400), but I can only and would only want to operate at KT333 for performance reasons. In my case that memory is a little overkill as I have not had much luck overclocking yet (I will get down to the bottom of what the problem is at some point).
The Gigabyte board has not received good reviews at overclocking either. If you plan on putting in more than one DIMM, anything beyond PC2700C2 is probably overkill. Now with all the memory pickiness of KT400, overkill may not be a bad thing. I would probably recommend the PC3200C2 anyways as the price difference is not huge and probably worth it for the extra safety margin. However, it probably will end up being overkill and not utilized anymore than PC2700C2 would be.