My friend is looking to upgrade his rig. Here are his specs: i7 3770 (Non K), 8GB 1600Mhz Ram, Gtx 560, Some H77 Mobo and a 320W 80+ Gold PSU. He wants to get a Gtx 670 or 760 but he doesnt know if his PSU is big enough.

You might need a bigger PSU. Probably like 500w+

When it comes to Multi-Monitor Setup AMD GPUs are much better. When it comes to a Single Monitor Setup Nvidia GPU's are much better. But then again you have to consider What games does your friend play?

Definitely a new PSU. 500W on the safe side, but you could run the 760 on 450W

I third the PSU option.