I recently upgraded from a BFG 9800gtx+ 1gb to an EVGA GTX 460 1GB Superclock. It's a great upgrade, but I can't imagine doing that from your sli setup. It's hard to tell exactly, but I think I got more than 50 percent more performance in games (especially BFBC2) and so I'm happy. I play on a 24 in monitor. However, my old card was still a decent card and anything less than a 460 would have been a waste of time.
I recommend you go SLI 460's. Check back and let us know, plus maybe some benchmarks- I like to compare Far Cry 2 DX10 on mine.
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