With the FIS, if you want to use DDR 400 and all three slots, MSI recommends that all three DIMMs be single sided. For any other combination they recommended dropping the speed to DDR 333. The ASUS K8V SE doesn't recommend DDR 400 at all when using all three slots. If you need more than 2 slots, you should probably look at the manuals to see if they support DDR 400 when using all the slots.