All GFX cards are made from the same reference design, with the major differences coming with the software each company includes for overclocking. So, if you don't care too much about overclocking, go for the cheapest pseudo-reputable card.
If you care about OCing your card do a little research. And if you don't consider yourself very educated on the subject don't try for a high overclock or you might damage things (in outlier cases, it's just nice to know what you are doing).
The 560 is an architectural upgrade over the 460 with higher pixel clock, shader clock, and memory bandwidth. You should see anywhere from a 8-15% improvement per card. The EVGA card you linked seems like a decent choice, and with 2 in SLI you should be comfortable playing any game at max settings on a 1920x1080 resolution screen.
I'm a big fan of modular PSU's, and I think 750W is probably fine (Eyeballing it you will probably max load around 600-650), but that PSU is pretty expensive and doesn't have great reviews. Consider this PSU (I like corsair):
I have an XFX 750watt black edition PSU. I love this thing to death. It handled a pair of overclocked GTX 470's and a pair of GTX 580's with no problems. Silent as a mouse.
Most corsair and XFX PSU's are made by a company called Seasonic. If your PSU is made by Seasonic, its awesomeness is guaranteed. plus a 5 to 7 year warranty. I got the XFX over a Season and Corsair branded PSU's because of the price, it was on sale on Newegg. Got it for $75 when its normal price was $125.
Avoid OCZ like the plague.
Those Evga cards will be beasts. I would take em. Nothing will be out of your reach, even 3D gaming.
OK, I've never done SLI before and I'm a little concerned after googling it. This is my work computer as well as gaming so to maximize my efficiency I use 3 monitors. The left and right monitors are both standard 24" LCD's and don't have anything really intense on them ever, just EXCEL and our shipping program. The center monitor is where I game and it is a 23" LCD 120hz Viewsonic. I just assumed I could plug all 3 monitors into the 2 560's and I would be able to 'focus' the power on the center monitor, is that not correct? Do I need a 3rd GPU to just run the 3rd monitor, just a cheap little card or something? I want the full power on my center 120hz screen but still need my other 2 monitors to be able to run when I'm not playing games. Was I ignorant to assume I could use all 3 monitors on the 2 560's?
OK, I figured that out. I'll be adding in a 3rd GPU (a cheap little 8400) to power the 3rd monitor. My new question is should I have BOTH my left and right monitor in the 8400 so that I can focus both the 560's on the center monitor, or does it not make a difference if I have 2 monitors or 1 plugged in.
You have room for 3 GPUs? You can plug your monitors in any way you want and it will make little difference. Sending a frame of video to a monitor isn't remotely close to the hardest job a GPU has to do.Even if you cloned all 3 screens when you game, it will not make it any harder on the cards.