What about the 6670? And how much quieter vs. how much less performance?
Quieter? About 40-50% less than a 560 Ti
Performance? About 60-70% less than a 560 Ti
But like I said, a 5670 or 6670 would be more than enough for a PC thats just playing back video on 2 monitors at 1080p, my friend has a 5570 and has a 2 1680x1050 monitor setup, works like a charm!
Also be sure to get the 1gb version of either the 5670/6670.
Also since you asked if the 6670 is better, simple answer yes.
Is it A LOT better? No, just about a 10% increase. but it MIGHT be a bit louder.