Most everything of import in this decision has already been said here ... So, I'm just going to add that, when you get right down to it, the 'better' choice is going to depend on what specific game you play on the rig, and what settings you play it at.
Also, it seems like, if video rendering is important to you, the 2600 would be worthy of your consideration as well, seeing as how it does the hyperthreading and all. Also I'm pretty sure that, despite the extra 2 cores on the AMD chip, with both at max OC's, the 2500 is actually going to be the faster of the two for the purposes of rendering as well.
Personally I'd be inclined to go with the Sandy/560ti combo if I were in your shoes. That way if you ever decided to go SLI, you'll be in fine shape ...
IOW, whilst I think that the 1090t is totally adequate for one 560, it's a little bit on the slow side for SLI 560's. Not that it'd be a big BN or anything, but there's a number of CPU-dependent games where it would be noticeably slower than an i5/i7.
Lastly, the 570 is really not that much faster than the 560 anyways Edited by brettjv - 5/27/11 at 10:20am