If you look at the benchmarks provided by Tom's Hardware for the GTX 670:http://img594.imageshack.us/img594/2237/gtx670sli.pnghttp://www.tomshardware.com/reviews/geforce-gtx-670-review,3200.html
You won't hit 60 FPS if you plan on playing at the highest resolution and very high settings with a single card. But with dual cards, you will be above 60.
Thanks, i think i might purchase a 1080p monitor instead, as i cant afford 800$ on graphics cards. 60 fps is better then a better picture, if the better picture runs poorly.