3d Graphics Crashing

Hello,

I have had these problems for a while so I am going to try asking here.
I crash (total system lockup) in Warhammer Online and recently in APB, usually after 20-50 minutes. I can start the software and step away from it, it will eventually crash with no user input.

I never crash otherwise.

Both applications are 3D-enhanced MMO games. I don't play other 3D games. At high settings the framerate is fluid but will lock up more often.

The last two nvidia cards I used were an Asus GeForce 9600 GSO and now an EVGA GTS 250. Both have the same behavior in the same games.

I have 'downclocked' these cards as much as possible, to avoid crashing, as suggested on sites. But it doesn't help. It seems the only thing that helps is lowering resolution to the point where I am looking at a game that is over ten years old (completely unacceptable) instead of much nicer at a normal resolution.

For OS I used Windows XP Pro x64 with latest drivers. Now I am using Windows 7 Pro x64 with latest drivers. The same problem happens on both.

The temperatures are stable and there are enough holes and fans in the case in an AC'd room to not worry about it.

My next step is to give up on Nvidia and try ATI. If ATI also has these system lock ups, I would then try a different motherboard, cpu, ram, etc.

If anyone has suggestions that would be great. I really want to be able to play these two games without crashing, so I am willing to do whatever is needed, but I'd like to avoid lengthy trials and returning of hardware.

Gear:

Asus GeForce 9600 GSO
and/or
EVGA GTS 250

Mainboard Asus P5Q
Memory: G.SKILL 8GB (4 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500)
CPU: Intel Core 2 Duo E8400
Power: CORSAIR CMPSU-650TX 650W
HDD: ICH10R RAID0 SATA drives 2x150MB