SLI/Xfire on C2Q or Phenom II

[chpctech]

I have a Phenom II 955 BE @ 4.2ghz on water
a Core 2 Quad Q9650 @ 3.8ghz on water
12GB RAM total (8gb in C2Q, and 4GB in PII)

I have a GTX460 1GB (not the SE ver), as well as a GTX560ti. The C2Q supports Xfire, the PII supports SLI. I am within my grace period to return the 560ti and was thinking about getting a Sapphire 6950 Toxic card for $290 shipped when it comes back in stock.

I need to sell one machine because I really don't need both right now, both have legit versions of Windows 7 on them. Should I keep the Phenom II and SLI (2) GTX460's, go with the C2Q and get the 6950 2gb, or stick with the 560ti and SLI later on down the road with the PII?

Realistically both machines perform about the same CPU wise and I can put 8GB in either one that I keep. It's an AM2 board so I'll have to upgrade m/b to go to bulldozer, or upgrade the lga775 to go to sandy bridge (possibly lga2011 later next year). Either way it'll be a new system when I upgrade CPUs so don't take that into consideration.

 

[chpctech]

Oh, I have BF3 preordered, and I'm very much looking forward to the next Metro 2033 game as well just as an idea of the games I'm looking to play. All on a 1080p monitor.

 

[Onus]

Assuming the AM2[+] board is fairly old, it may only run at 2000MT/s which could be one reason that SLI with AMD doesn't perform all that well.
Given that you're going to get a new mobo/CPU/RAM at some point, I would see what single card meets your performance requirements today, and go with that. Test the 560ti in each rig with your most demanding title/settings and see if there's a difference; go with the stronger one. Only swap the card if benchmarks show that your games favor AMD over nVidia, otherwise you're just turning in six to get half a dozen.