I would die for a p5q-pro, i only have a p5ql-e... I've heard good stuff about that board. I don't know why that mobo won't let you past 3.0ghz. My p5ql-e can go past, windows just crashes like a bitch. But thats understandable with a P43 chipset.
If you can't push your Q9550 past 3ghz, you unluckily have an unoverclockable chip, slow RAM, a stock heatsink, or you just plain suck at overclocking. No offense to any nvidia chipset users but the P45 chipset seems to overclock better than 780i, not on that particular motherboard, but in higher end motherboards. That P5Q motherboard should overclock good enough.
I had the CPU @ 3.47 GHz stable, back when my rig was new. But then Vista was f***'d - reinstalled - and then the clock was unstable, when passing 3.2 GHz, and after getting Windows 7, I can't even push it over 3 GHz. - Sounds wierd...?
I'd bought a P45 'cause of the overclock utilities, and performance.
BTW, my Q9550 is a C1.
I got the Corsair XMS2 Dominator @ 1066 MHz (1059 right now, cause of overclock...) 5-5-5-14 (15 is stock), with the fan.
On the CPU I got a nice little NorthQ 3580 Siberian Tiger... newbie watercooling system, but it's cool! Otherwise, I've 5x Noctua NF-S12B FLX's in my NZXT Tempest. So temps should be a problem either.