GTX 670 SLI vs GTX 680 vs?

Ok so right now I am looking to build a PC( and I have picked out EVGA GTX 670 SLI but I was wondering if a single GTX 680 would have near similar performance(like 5-10%) of the GTX 670 SLI. Because I'm looking to save some money right now. Would it be worth it now to just get the single GTX 680 and then later down the road do a GTX 680 SLI or just go for the 670 SLI right away. Or does anyone have any other recomendations of other GPU that would have similar performance at a cheaper price?

to go SLI would depend on your other parts but with GPU boost and easily overclock; I would wait for January sales and pick up a 680 and that will leave you open to go SLI in the future if a single 680 won't cut it, what resolution are you planning on using? 

If it's 1440p get the 670SLI if it's 1080p a single 680 should handle all games fine until you feel the need to get another in the future.

Yes I plan on using 1080p. And should I go with a 4GB or 2GB 680?

4gb only if you have a huge display

4gb for multi-monitor/3D/ heavy mod game saves, I myself am buying a 4gb 680 as part of my first build in a couple of weeks so if you want me to do some benchmarks when I get mine setup I can do if you still havent decided.

Well since I won't be doing multi-monitors I am most likely just going to go with the 2GB 680. But if someone can run some benchmarks of the 680 for me I'd really appreciate it.

there's plenty of video benchmarks on youtube but most are 3 months + old so any new drivers could improve it, I will have my PC ready around 21st Jan so can't run any benchmarks until then.