Should be fine. The 480 is power hungry but shouldn't need more than a 500w for one. Even though the TDP for the 480 is 250w. Plus the 965's 125 puts you at 375w and maybe 25w more for the rest of the system. You should be fine. Maybe a 600w would be needed if you want a safety net.
It's a matter of how many watts the PSU can throw at the 12V rails. I looked it up, and the CX500 can put 408W toward the 12V rails. That leaves roughly 150W for not only the CPU, but all the other things in your system that use 12V. It might be fine, but it would seem to be pushing it to me. But if he's going with the 600 watter, then there's no need to worry.