BSOD during/exiting/alt+tabbing games, streaming video

Good evening-

I've been experiencing BSOD's at an increasingly frequent rate since early July. It only seems to happen when I am playing, alt-tabbing out of, or exiting online games (GW2, FFXIV), or streaming video. The most recent BSOD took place last night during an FFXIV session. The most common error messages are system service exception and system thread exception not handled, though there have been a couple of others.

Once the BSOD's started, I downloaded Nirsoft's blue screen viewer - almost all of the crashes are linked to ntoskrnl.exe, nvlddmkm.sys, and dxgmms1.sys. The real issue is that the problem is fairly intermittent - one crash per 2-3 days. When I had a ram stick die on my last year it was pretty simple to diagnose, but I've proven unable to track this one down using my normal methods. Research online hasn't pointed to any specifics so I thought I would ask some experts for help.

Things I've tried so far:
Uninstalled all drivers and programs installed since the blue screens became frequent in June.
Updated nvidia drivers.
Ran chkdsk and virus scan with no hits on either
Updated BIOS
Ran memtest for 4 passes (about 2 hours) with no errors
Discarded an old, unsupported USB headset (which I thought was the culprit until a few nights ago)

I am not a very accomplished debugger, so any help you guys can provide would be greatly appreciated.

System Specs:
AMD Athlon II X4 640
ASROCK 870 Extreme3 R 2.0
8GB Kingston RAM (Four 2GB sticks)
NVIDIA Geforce GTX 460
Seagate Barracuda 300Gb HDD
Thermaltake Toughpower 650w PSU

Thanks.

Update:

I realized that I had beta nvidia drivers installed and rolled back to 320.49 WHQL, which given that I had that driver installed during several BSOD's might not fix the issue, but I did do a clean install of the drivers during the rollback.

Hoping to play FFXIV later tonight, so I will update with another dump if I crash again.

Reinstalled Windows, thus solving my issues.