Im thinking of upgrading my GPU and the PNY GTX 660 is cheap and I hear it is good. If i link two with an SLI bridge will it perform well or should I save for two of the MSI 760s? Now I also plan on a new motherboard, the Asus Sabertooth with AMD, but that's for another post. Games I play are: Syndicate, Titanfall, Blacklight: Retribution, Solar Conflict, Half Life and Portal.
If I were you I would get one GTX 770 for those games a single GPU will give you better performance. Those games are also not really demanding games so you most likely don't need 2 760s.
i personally have 2 evga 660s in sli. and the only downfall for me is some of these steam alpha games dont use sli. other than that it works great.
I agree with raging4vok. Just buy a GTX 770 and save yourself the headache that is multiple GPUs. And if you are gaming at 1080p the 770 will be more than enough for quite a while.