Let me get this: You guys all agree, Q9400 OC 3.8G upgrade to i5 2500K OC 4.4 won't gain a lot performance increase. (gaming wise) Also spent $400 is not worth to gain few FPS upgrade CPU and MB, if I keep the GTX 560Ti.
Because of my P5Q Pro's limitation, I can't run SLI. So I'd better sell my GTX 560Ti, to get EVGA 560 win 2 or CF 2 ATI (6870 OR 6950 2GB). Or matbe wait ATI 7000, Nvidia 600 and IB.
EDIT: Doh I see your res on the first post. I'm blind..
Upgrading your CPU right now won't gain much, as already stated. But consider, once you start upgrading the motherboard, you are throwing more money after old technology. So consider it first.
I do not agree with buying the win 2 card, that is a waste considering you _already_ own a 560 Ti, any way you cut it. You'll lose some money selling your Ti to buy another card with 2 x Ti. 1GB VRAM will be ok for 1920x1200 in my experience. So don't write off 1GB cards. In any case, the Ti 2 Win card is not a value card and won't add up dollar-wise.
You are in a bind, sort of, because you have a pretty good card already, so your only single GPU options above the 560Ti are out of the value category and into the premium category (570, 580 or 6970). So its either spend money on premium cards, or SLI or Xfire, so look at your options:
1) Buy an SLI capable LGA775 motherboard + a 2nd 560Ti for a massive performance boost for $330 total minus selling old motherboard for $40 =
$290 total
2) Buy a higher end, single GPU card (570) for maybe 10fps increase for $300 minus selling 560ti =
$120 total
3) Buy the single slot Ti 2 Win card for $550 minus selling 560ti = total expenditure
$370 total
So there you are. (1) will net you a huge boost for $290, (2) will net you a minor boost for only $120, and (3) will net you the same as (1) but for $80 more.