As xbb said above, the GTX 460 is not supported yet. If you are looking for a Radeon card, of the three choices above, definitely go for the 5870. The single 5770 does not exceed or even match it in performance, and the 2 5770's just barely match 1 5870. With the 5870, setup will be easier then 2 5770's, and you will require less power and produce less heat then 2 cards.
But, about the GTX 460, it's all up to you. You can get it and wait for support to come(Although it may never come), like I am, or just not get it at all. I love the card(In windows and linux at least.) because it can keep up crysis warhead on gamer settings on my 1080p 23.6" with a clear 30FPS, and the card is only 199 or 230 bucks. Not to mention the temps at full load do not go over 75 C(And this is with EVGA's FPB and my 9800 GT at full load in the same case). It's an awesome card, although it would be even better if I could get it working in OS X. Here's to hoping it come with 10.6.5(But I doubt it).
If you want, read
this article by Tech Report. It ranks ton of cards together in benchmarks. Not only that but it also shows 2/3 card configurations of CrossfireX and SLI.