It honestly depends on what budget you are on. If you already have a 460, it'll cost as little as $130 USD to get one, but SLI 560s will cost from $350 to $440 USD. Dual 460s will have no problem playing anything (including Crysis 2 DX11 Ultra) so there's no problem in getting one. However, you're going to have to replace the entire setup when another graphics upgrade is in order. But at that point, you might as well get a new rig.
Definitely another 460. 560 is just a 460 with a newer chip. http://www.tomshardware.com/reviews/geforce-gtx-460-sli...
If I'm interpreting Tom's charts correctly a pair of 460's in SLI scale up to 190% over a single card.
then, looking at the BF3 charts that would suggest 77.4 FPS in BF3.
470W at full power, 160W @ idle. 78C on auto fan.
Anyway, that's why I decided to SLI my 460
Sli 560, the 560 is a 460 like delroy said but it's better with power/temps. On the other hand is that worth the extra bucks ? If i had a 460 allready i would go for sli460. Can't you sell the 460 and put that extra money in a 560Ti and sli that later, that would be really best.
Two GTX 460s will out-perform a GTX 570, two GTX 560s will out-perform a GTX 580. I'd recommend that you SLI the 460 and save for a later upgrade when the 600 series comes out next year. That way you skip a generation.
go for gtx 560ti sli but you have to need a good psu and gtx 460sli is also a good solution but tell me one thing why dont you buy gtx 580 or 590 instead of sli 2 medium cards as compare to these high cards?
I'm going to SLI GTX 460's 'cause I already have one. Just as soon as I get the RMA straightened out. New one ran but wouldn't show in device mgr. and didn't install on 'adding new hardware'. Ran one pass of Unigine Heaven and I could have fried bacon on that sucker!