If that PSU wasn't Antec Earthwatts I'd bet 10 bucks for PSU failure...
I had same issues with my Q6600@3.6 GHz. And strangely enough it was only happening in BF3. My problem was not enough voltage on CPU*. However, after doing research and digging over net and talking with my techie friends, I saw those 124 BSOD screen are often related to PSU not working as it should.
I think those multiplayer FPS games are putting almost full load to CPU&GPU all the time. That stress whole system and PSU beyond syntetic single stress benchmark could ever achieve. And that causes errors..
Imho, if you have a chance to test with different PSU, go for it.
*: The actual problem was, not stable voltage on CPU's VCore. I blamed my mobo's voltage regulators but apparently, it was my OCZ StealthXStream 600W's fault. I reached that conclusion because, I found same symptoms in almost same setups that are same age and overclocking status with mine. The problem vanished after PSU swap on their systems.. That PSU is still serving me in my new system tho. I guess new system is not asking that much watts as older one.
firstname.lastname@example.org GHz, Noctua C14 to keep it cool, ASUS Z68-V PRO/GEN3, 2x4 GB DDR3-1600 G-SKILL RipjawsX, ASUS GTX560 DCII TOP@925/1850/2000(RIP MSI GTX460), OCZ 600W, 1x256GB Samsung 830 SSD, 2xSamsung 1 TB RAID 0, 1x2 TB WD Green, NEC 7173-S, Enermax Chakra