Dual graphics cards for performance boost

[tasumai]

So Long story short. Here are my specifications of my current build:

intel core i7-930
asus p6td deluxe motherboard
24gb 1866 (O.C.) Ram
900 watt quad rail antek power supply
256 SSD intel 530
3 - 24inch LG IPS 1080p monitors
Windows 8.1 Pro

the GPU I am currently running is the ASUS 7970 directCU II 3gb graphics card, now it came to my attention that I can run two of the three slots at a x16 performance. (x16, x16, x1) capability. and while I would love to simply crossfire two ASUS 7970 3gb cards, I cannot afford such a luxury. but I do have two EVGA 2gb Geforce GTX 560 lying around. I would like to utilize both cards not for display power (because I am aware of the fact the asus can handle 6 monitors and the 560 can only handle 2.) but I am wanting to output better performance.

Is there any benefit to me running the Nvidia and AMD (AMD primary and Nvidia secondary of course) or would I get better performance with dual 560s in SLI?

 

[clutchc]

If you are referring to gaming performance, The single HD 7970 w/3GB would be smoother and nearly as fast a 2 x GTX 560 2GB cards. (Maybe faster depending on the games' ability to utilize SLI. Not all games are optimized for it. Plus, you'd loose the extra GB of VRM for better A-A, AF, DoF, textures, etc. I'd suggest you try it both ways and see for yourself, tho. Me, I'd use the GTX 560 for the 2nd monitor.