So I’ve just bought a GTX260 to replace my 8800GT.  I suspect this will push my PSU to its limit but being of Dutch heritage I’d prefer not to have to buy a more grunty one unless I absolutely have to.  On-line PSU calculators suggest I may be OK but getting close to marginal.  System is rock-solid at the moment. 

Is there a a reasonably reliable, and safe, way to confirm whether my existing PSU is up to it.  I’m thinking along the lines of installing and running some iterations of 3DMark, or similar that pushes the CPU and GPU towards some of their upper limits.  If the machine doesn’t crash (or catch fire) it might be OK.   If it does fail somehow, time to open the wallet, watch the moths fly out, and spend some cash on a new power supply.

 Not a particularly scientific approach.  Any better suggestions?

 Rig specs:
Q6600
2 x @GB DDR2 RAM Sticks
2 x SataII HDD
1 x SATA DVD/RW
8800GT (old, to be removed)
GTX260 (new)
1x Firewire Card
1 x TV Tuner (happy to take this out if it helps, don’t really use it these days)