During a game of Crysis 2 I measured the maximum consumption for the whole computer, but it was only 252W. This game was most energy-intensive than any other 3d games. My pc is i5 2500K at 3.3GHz(not OC), MB H61, 2x4 DDR3, Sapphire 6950 1gb, hdd WD 300GB + 150GB, DVDRW Pionner and Fortron 700W 80 gold.
I think your PSU is enough to handle with your PC.
I had a PS go bad on me. Replaced it with a coolmax 650 with 38amps on the 12v rail.......... 6950 2gig/6core/4gig, etc....... but this runs XP and the card is swapped in for testing. So far so good but I like to run something with more amperage for stability and honestly a little cooler running. The harder they work the hotter they get. you might get away with it for a while. Games played@1920x1200...... FarCry2-NFS Shift 1&2-Crysis-HardReset demo and a slew of older Quake based games.
A 6950 needs about 12 amps peaking to 15 amps under load. If you have an OC'd quad core CPU, that's another 10 amps.
Your PSU is rated at 34 amps (typical for a 500 watt PSU) on paper, but Raidmax PSU's tend to be overrated.
I think your PSU can handle the card, but I don't think you will have much reserve left over.
One of my systems has an OC'd Q9550, 4 GB RAM, a GTX260 - a card with similar power requirements to yours, a Gigabyte EP45-UD3P motherboard, 3 hard drives and an optical, and a Soundblaster card all powered by a Corsair TX750.
Running 3 instances of Prime95 to load the CPU and 3DMark06 to load the GPU, it pulls 375 watts from the wall as measured by my Kill-a-Watt meter. Figuring 80% PSU efficiency, the system pulls 300 watts from the PSU.