Here's couple in-game benches before I change the pumps.

All in benchmarks run with:
Settings: Maximum
AA: 8x
Resolution: 6000x1080
Stereo: 3D

1) Mafia II
Average: 32.5
VRAM Usage: 1050

2) F1 2010
Average: 39
VRAM Usage: 2600

3) Just Cause 2 - Desert Sunrise
Average: 34
VRAM Usage: 1300

4) Dirt 2
Average: 53
VRAM Usage: 2200

All run @ my OC 24/7 settings, great results in my book - considering such high res in 3D - finally everything playable on max!

There are other great side effect to these 580s too:
- no more flicker in side monitors in 3D Surround (there was pulsing brightness change with 480s, not sure why, I could live with it but it was annoying)
- no more black textures in the distance in Mafia while driving