Re: Need some upgrading advice.
260s in SLI would be significantly stronger than a single GTX. And you wouldn't need anything more than a 750W quality PSU to run them with.
I might would hold off on the CPU upgrade until you get a new board. I doubt you'll hit 4GHz on an 8500; I remember that board of yours being really quirky when it comes to OC"ng. I used to own it if you remember. In addition, Intel's new X58 is on the horizon that will support SLI.
i7-2700k @ 5.0 GHz
Nvidia GeForce 570 2.5GB Tri-SLI
Asus P67 WS Revolution (Tri-SLI)
OCZ Vertex SSD x 4 (Raid 5)
G.Skill 8GB DDR3 @ 1600MHz
PC Power & Cooling 950W PSU