@BaboonGuy - Make sure you run the tests long enough. If you've run memtest and it passes all the tests, it's probably not bad RAM. So let's then look at CPU test like Prime95 or OCCT. For a quick check, run them for an hour or two, but to ensure it's *really* stable (and with what you're doing... you need stability) run them longer. Personally, I use OCCT 1hr for my quick checks, and then i run prime95 for 8-12hrs checking for stability. Some people run them for 24hrs+, it depends on your comfort level.
I'm not sure what is a reasonable voltage for that chip, somebody else will have to chime in on that. You will see different values in BIOS vs CPU-z. I'm pretty sure CPU-Z is what you want to go with since the BIOS is what you set the board to, and CPU-Z is reading what you're actually getting.
@ccbadd - XPx64 was plagued by driver and application compatibility problems. Little stuff like printers wouldn't work, or scanners, lots of programs, or whatever. Check the Adobe forums for issues with XPx64 and Adobe compat problems, there are TONS. According to the OP he is using photoshop, and might also be using premiere for video (I'm guessing that). Both have tons of confirmed issues with Xpx64. CS3 didn't support 64-bit windows of any flavor, but people were able to get it to work with little to no troubles in Vista x64. I'm pretty sure CS4 "officially" supports 64-bit Vista, but not XPx64.
Since the choice at the time was XP 32-bit (no problems, but you lose ~0.5GB of RAM) or XP 64-bit which would give him access to all his RAM but would *more than likely* put him in a world of hurt for his software I chose to recommend the former. Vista x64 is much better than XPx64 (IMO), but at this point Win7 is right around the corner. So my advice is to stick with XPx86 for now and lose out on the .5GB of RAM until Win7x64 comes out.