p5e3 and pkq3 won't go over 400fsb

My current rig is in my sig. I also have a p5q3 board as well and it seems both of these boards get very unstable past 400fsb or so even with more voltage to the NB. I highly doubt its just a coincidence that both of these boards have the same fsb wall. Can anyone suggest anything else to try? I have done pretty much everything I could possibly think of (voltages, ram timings, kicking ram speed back, lowering cpu multiplier).