got an asus p5q myself had same problem. got around it by turning the mounting bracket 180. only down side is you can't use memory slot 1.
no dice, rotate it one way, it hits the NB and SB heatsinks, rotate it the other way, it hits the capacitors. ended up returning it and bought a Xigmatek Dark Knight S1283V which fits well.
Specs are now at:
Q6600 @ 3.20 GHz (8X400) at 1.29V CPU voltage
TEMPS: Idle - 32C, Prime 95 100% Load - 57C
Room Temp is at 72F
So far so good. Did 3 hours of Prime 95, no errors so far.