Since you’re buying a GPU to sell it in very near future, you can go for a second hand purchase. This way, you wont lose much, as Purchase price(used)-Sell price(5 months further used) would be quite low. Also, this will open some exotic powerful options like the GTX 260 216c (~6k), Cheaper GTS450 (~6.5k), which will drive the 2x(1920x1080) at native res without dropping many frames. So, when you sell it at 1k-2k loss, you will still have ample money saved for the GTX 560 Ti. Moreover, the upgrade steps would make quite alot of sense => 7600GT > Used GTX260 > New GTX 560 Ti.
As for the PSU, a VX550 is the perfect choice. Shear quality, not a vicitim of the recent Corsair cost cutting.
So, my opinion:
PSU (4.8k) + GFX Purchase GTX260 (6k) - GFX Sale GTX260 (5.5k) + GFX Purchase 560ti (Less than 10k) = Around 15k
If looking for a new purchase only, then following is recommended:
PSU (4.8k) + GFX Purchase GTS450 (Lower performance than GTX 260) (7.2k) - GFX Sale GTX260 (5.2k) + GFX Purchase 560ti (Less than 10k) = Around 17k
Assumption: OP wants Nvidia only