Read pages 233, 234, 235 at the q9550 Club thread
...wherein I write with detail how to overclock your Q9550.
As for GPU, it depends on your budget. GPU's follow sorted in order of more expensive to least expensive:
Nividia GTX 780>ATI Radeon HD 7970 GHz Edition>Nividia GTX 680>Nividia GTX 660 Ti Boost
Q9550 is decent for BF3 only if OC'd to 4GHz and above. To do 4GHz in the summer with 35C ambient with your Q9550 and to cool it adequately, you need a really good CPU cooler. Again, it all depends on your budget:
Coolers follow sorted in order of more expensive to least expensive:
Noctua NH-D14>Thermalright Silver Arrow>Thermaltake Frio OCK
I am using the last one, and it is sufficient to to keep my CPUTIN temperature below its Intel TCASE temperature of 64.5C and my ambient here is 35C. My QX9650 is OC'd @3.85 GHz for the summer.
You need to keep your CPUTIN temperature below 71.4CC b/c your CPU's specs are different than mine. CPUTIN (not Core) temps above 71.4C will degrade your CPU.
Your MOBO is an Intel P45 MOBO and as such it is decent. Nobody is using Intel MOBOs so nobody can tell you exactly how to OC your MOBO. 95% of users use either ASUS or Gigabyte MOBOs. Just read the thread above and follow the general guidelines I outline there.
P.S.: As the poster above me noted, if you buy a new GPU and you overclock to 4GHz, you will need a new PSU. A Q9550 at 4GHz draws approx. 151W from the mains, and at 4.2 GHz approx 194W from the mains.
I recommend a PSU around 700W if you go with a GTX 680/780 or Radeon HD 7970 GHz Edition.Edited by Arxontas - 6/23/13 at 9:47am