A GTX 260 SLI equals a GTX 470 performance wise. I actually had the same setup before I moved to the newer 470. And they basically benchmarked identically.http://www.tomshardware.com/forum/292068-33-benchmarks-core
If you have a GTX 260 now, and can pick up a second one fairly cheap it's a great performing setup. And it'll easily outperform a single GTX 460. And does well @ 1920x1200.
However, if you'd like to have DX11 capability the GTX 460 would have the advantage there. The games you listed however aren't games that I'd spend money on just to get DX11. Starcraft 2 is the only one new enough to even take advantage of DX11, and honestly I don't think it would make a big difference. Some titles, like the new WoW Cataclysm have optimizations to improve performance using DX11. But most games it's a performance hit.
Should you get a GTX 460 however (or your friend) check out the MSI Hawk GTX 460 @ NewEgg.com right now.
It's a good deal with rebate and such.