1- I'd go with the i5-2500k, is better for price/performance.
2- You save some money with the i5-2500k, so, go with the GTX 560 Ti
3- 850W is a little overkill, but I'd say that you are thinking in future , Seasonic, Corsair, XFX, Antec are trusted brands.
4- ASUS P8P67 Pro or Gigabyte P67A-UD4
Regarding the upgrade time, you can use it for not more that 3 years, more when Ivy bridge comes out.
Total of $933 not including tax so probably around $1000
I still have my GTX 295 running strong so i'll probably won't upgrade that just yet. I had the GTX 580 but i ended up giving it to my brother as a gift lol. Kinda want to wait till something better then GTX 580 comes out that's not a duel gpu. Maybe 6-8 months they'll have a new one. I'll get another 4gigs of ram if i need it and i'll buy a set of SSD's when price drops.
That build is great (aside from PSU), but you sound like the type that wants the best.
I'd go with a Corsair, XFX, Antec, Seasonic, or Silverstone PSU. I'd also get a $50 cooler that already had fans.
But as far as what I was saying about the best...why not wait until the X58 replacement comes out if your current build makes use of the GTX 295? Otherwise you'll end up thinking you don't have the absolute best out there. And that could end up mattering with top end cards. 8x/8x PCI-e speed that you get with the better 1155's (such as ASUS PRo P67) might not be good enough.
I'd also spend $120 on a SSD before a $500 graphics card that replaces the 580--considering that that means the 580 would drop in price and you really don't need anything better than that. I mostly mean the SSD would improve your enjoyment of a computer more than a graphics card better than the 580.
A bit over your $1000 limit at $1167 .... but sized for twin GFX cards. Drop to the 460 and drop the cooler if ya need to hit $1000. W/ stock cooler ya can hit 4.6 GHz. The Black PSU is the equivalent of the Corsair HX / Antec CP or SG and is well suited for providing stable voltages w/ twin GFX and hi overclocks.