BSOD 0x00000124 - Crashes under heavy load

Hoping someone can help me diagnose my system's instability. Recently, after installing and playing some of the BF3 Beta, my system began to crash. As I had just installed a new version of the ATI drivers I assumed that was the issue and rolled them back. No joy. Then I installed the preview version of the ATI drivers suggested by EA but my system continued to randomly crash.

After some troubleshooting I eliminated the RAM by running several clean passes with memtest86+. All of the other components seem to operating normally as well, so I turned to the CPU and torture testing with Prime95.

If I run all six cores the thing will crash immediately. It won't run for more than 30 minutes on any more than three cores, and no more than 15 or some on any more than four. I have discussed the issue with AMD support and they pointed to the PSU, which was only 520W. I upgraded that to a 850W PSU but that had no effect. AMD has offered to replace the CPU but A) I'd be without a CPU for over a week waiting for the replacement and B) I hate doing that if I'm not positive it's the problem.

I'm hoping the minidump will point to the exact cause. I've also removed the heatsink and fan, cleaned off all the thermal paste and reseated everything. I had put far too much thermal paste on when I first built the machine. Sadly, that had no effect. I've also monitored my CPU/mobo fan and heat levels during testing but they never get much higher than 42C so I don't think heat it an issue at all.

Any help would be appreciated - what a quandary!

BTW, here are the system specs:
1 x GIGABYTE GA-990FXA-UD5 AM3+ AMD 990FX SATA 6Gb/s USB 3.0 ATX AMD Motherboard
1 x OCZ Vertex 2 OCZSSD3-2VTX90G 3.5" 90GB SATA II MLC Internal Solid State Drive (SSD)
1 x XFX HD-687A-ZNFC Radeon HD 6870 1GB 256-bit DDR5 PCI Express 2.1 x16 HDCP Ready CrossFireX Support Video Card with Eyefinity
1 x Kingston DataTraveler 101 Gen 2 4GB USB 2.0 Flash Drive (Cyan) Model DT101G2/4GBZ
1 x HITACHI Deskstar 7K3000 HDS723020BLA642 (0f12115) 2TB 7200 RPM SATA 6.0Gb/s 3.5" Internal Hard Drive -Bare Drive
1 x COOLER MASTER RC-692-KKN2 CM690 II Advanced Black Steel ATX Mid Tower Computer Case
1 x Thermaltake TR2 RX 850W Black Widow PSU
1 x AMD Phenom II X6 1090T Black Edition Thuban 3.2GHz Socket AM3 125W Six-Core Desktop Processor HDT90ZFBGRBOX
1 x G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL9D-8GBXL
1 x Logitech C910 USB 2.0 1080p HD Pro Webcam
1 x LITE-ON DVD Burner - Bulk Black SATA Model iHAS124-04 - OEM
1 x Microsoft Windows 7 Home Premium SP1 64-bit - OEM
1 x COOLER MASTER Hyper 212 Plus RR-B10-212P-G1 "Heatpipe Direct Contact" Long Life Sleeve 120mm CPU Cooler Compatible Intel Core i5 & Intel Core i7