Re: 2x GTX 460 1GB in SLI vs. GTX 480
Well the good thing about SLI is you can set a profile to disable it if you do have issues with it in certain applications. Though obviously the downside is you won't get the extra performance. But any applications that have issues with SLI probably wouldn't need the extra performance since the 460 is a fairly strong card on its own.
Where the headaches come in is when the application could use the performance of two cards but has issues with it. When I had dual 8800s Empire: Total War had terrible issues with SLI and it was a game that could have used the extra performance from those cards. Though my thoughts are the game suffered from poor driver support from nvidia for those cards as the 200 series had no trouble with SLI but anything G80 or G92 just flat out sucked with SLI. So I guess down the line if you want to keep the card for a while it could become an issue, but partly it depends on nvidia's driver support.