It's nice to see that the GTX 280 (and similar Nvidia cards; 275/285) still can provide one hell of a performance when compared to newer cards.
I ran some bench marks with my dual GTX 280s on driver 260.99 a little ways back and then compared those results to the BETA driver 270.51 (about a 5-6% boost in performance overall).
I have a similar setup, this is what I used and what I did:
Ran 7 benchmark runs, eliminated out the highest and lowest result, then averaged out the remaining 5 runs.
CPU: Phenom II x4 940 @ 3.514GHz (16.5 x 213)
RAM: 4GB Corsair XMS DDR2 800 @ 852 5-5-5-18
GPU: 2x GTX 280 SLI (651/1406/1164)
MB: ASRock K10N780SLIX3-WiFi)
Video Driver: 260.99
Resolution: 1680 x 1050
Crysis (5 runs): DX10, Ultra High settings, AA 4x
Max FPS: 48.5
Min FPS: 19.5
Avg FPS: 37.2
Using the Beta Driver 270.51, here's the results:
Max FPS: 51.3
Min FPS: 21.1
Avg FPS: 39.6
That's the only game I ran that I can actually compare to what you ran, even though you had Warhead benchmarked instead of the first Crysis. My cards still pretty much crush any game I play them with, so I'm content with what I have. I would like to get new cards, but no money and the fact is, I generally don't fix what isn't broken. And my PC runs great, so no need to upgrade.
Thanks for sharing.