My first thought was PSU except for two reasons:
1 - Corsair makes pretty good power supplie sand 550 watt PSU is more than adequate.
2 - An inadequate PSU generally causes a clean reset/reboot (no BSOD).
My guess would be a defective video card or bad video drivers. I'd try to install the card into another system.
Perhaps its a cooling issue. I remember a few years back one of my AMD cpu's (cant remember which one) used to overheat under heavy load and the system would reboot, cant remember if it used to blue screen tho.
I'm getting BSoD and system restart often whilst playing DoW2. I'm running a 4890 with a 550w psu. Its also happened whilst under load in Gary'sMod. I've updated the latest drivers, cleaned registry. Would this be a GPU cooling problem? It's really giving me a headache.