The gtx480 is pretty sweet, but you can't SLI it in the future unless you buy a new motherboard. The 5850 and 5870 can be crossfired and will beat the crap out of the 480. I'd probably say if your power supply (and your wallet) can handle it go with the GTX480. By the time you find yourself needing more power to run games you'll be looking to build a new system and then you can SLI the 480s.
I would not buy a 470 or 480 due to them being shoddy design and overpriced. When they make cards with the 460 design but more powerful, then I would consider Nvidia.
I would personally grab a 5870 because I prefer a powerful single card, it can handle everything at the moment anyway and in the future you could then Crossfire it if games get heavy (by then the total cost will likely be similar to you buying two weak cards now, but you'd have better performance)
x8/x8 has very minor consequences to Crossfire and SLI so I would not worry about it
Indeed I forgot to mention the PSU - Corsair TX750 so I guess I have enough juice to go CF...
In general I also favor single card setup but I find GTX480 is bit too expensive, power hungry and noisy, so I want to hold from it (though my last 3 cards were all nVidia).
Currently I find ATI bit better overall...
So because of that I thought that 5850/5870 in CF would be good solution for now... but still has some doubts that x8 will be enough for 5870 in CF.
Look at the 2 way crossfire performance. This was done with 2 5870s. The x58 uses x16/x16, and the p55 uses x8/x8. They concluded that the x8 link only caused a 4% performance drop. Definitely not enough to worry about.
Thanks for the link... I also have done some extra research and indeed it looks OK for me to go with 5870 CF... Now I have to check again what are the prices of 5870 & 5850... I still wonder which one will have better bang for buck - 5870 CF or 5850 CF.
Best bang for buck will likely be the 5850 - top end card is never best price/performance. The question is whether or not you want more power. The 5870 is close to the 480 withut having the noise and power issues, so if in an ideal world you would have spent a fortune on the 480 if it had been designed well, you may prefer to sacrifice price/performance to get the extra power the 5870 provides.
I have a 5850 and I am happy with it, but, if I could have afforded it I would have induldged in teh 5870
In your situation with your motherboard I would recommend the 5850 crossfire. Just be mindful of compatibility issues of any crossfire or SLi setup as some games and applications have issues with them.
A GTX 480 would be a good solution too, it's just that it is very expensive and does produce a good amount of heat. Noise levels aren't as bad as most people claim, but they are higher than what you'd expect. Granted, if you picked up a GTX 480 with an aftermarket cooler, it could compensate for higher temps and noise levels.
But, I digress, I still recommend the 5850 crossfire solution. If you even really want, you can invest in some high end 5850's and overclock to match a 5870 crossfire setup.
I was in similar position some time ago when I got my GTX280... It was hottest and most powerful (single GPU) card at that moment...
Indeed after some time I change the stock cooler to the arctic accelero extreme and I'm quite happy with it. very quiet and cools superbly. the only drawback is that it is 3 slot... but since it is single card, no problems...
but now I would like to go the other route - 5850 soon enough and after some time if/when needed, I put another one...