GTX 460 SLI with GTX 480?

not sure where you heard that but no you cant.

Short answer is no. Both cards must be the same model for SLI.

I don't see that happening

A gf100 card and gf110 card will not sli. Ive only seen diff models within the same family sli after bios flashing but even then it was hit and miss. For 200 bucks get a 7850 or 7870, youll be very pleased with the upgrade.

Nope. You should just get a 480 and sell the 460 IMHO. Or use it for physX if there's any Hardware (GPU) PhysX games you play regularly.

I can sell you a 460 and sli cable if ya want

get a single 580/7870 used or new

2 x 460s would be fun, but I dont have SLI board, I do have 2 working crossfire systems.
Got a 460 on my Nvidia gamer/folder pc. Used a gts 250 for PhyisX but it interferred with the folding. It is a older asus crossfire 790GX that uses a switch card for video if you are running only one vid card. So I put in a GDDR3 HD 6770 (you know the low power ones without crossfire slot connector) in the switch card slot because I could not remember where I put the switchcard. Did NOT load AMD drivers. GPUZ says it is the PhyisX card. The Pmark is about 50 points higher with it in instead of the switch card. Stange It folds 1000-2000 PPD while the 460 is folding too.. It did not seem to make any difference in FPS when playing. The GTS 250 for PhysicX did not make any FPS difference either Playing JC2. I am pretty sure that a 460 has enough horsepower to do it all by its self. BTW a GTS 250 & a GTX 460 dont like folding on the same PC. Still dont know why. It may have something to do with way a 790GX AM2+ chipset works. I tried the Gigabyte 7870 in it. It works pretty good in that too.
The folowing is my round toit list:

I have not figured out how get the 7870 to fold
Thought about getting a SLI board just to play around with it.
But I will either get a 2nd 7870
replace the 460 with a 660Ti 1st?
Besides I am curious just what a Thuban plus 2 Xfired 7870s in a AM2+ system can do. Would you be disappointed to find that BF3 is playable single monitor @1080p on something that old? JC2 & ME2 play smoothly with maxed settings with the Gigabyte 7870 OC & more OC is NOT necessary.
Ok I can cross this off. Yes it works with 150 more clocks on memory & GPU but I dont need it unless I add more monitors.