2600k vs 3770k

Depends on what your friend is doing with the computer. If this is just for gaming, I wouldn't get either one. I would get an i5 2500K or a 3570K. i7s have HyperThreading, thats the only difference between i5s and i7s. Its great for productivity, but no game now, nor likely any game in the future will be able to use it.

The difference between 2500Ks and 3570Ks in gaming performance is nothing but price. That would free up budget for a stronger video card, maybe even a GTX 670, since the video card is where you want to go heavy for gaming.

If hes going to be doing heavy video editing and stuff like that then the i7 is the best choice, but even just the occasional productivity work, the i5 would be fine.

4.2GHz is a more realistic overclock target with Ivy Bridge and since IB has ~7% better IPC than SB, you would need a ~4.5GHz overclock on SB to match it.

Personally, I would go with 3770k but if your friend is obsessed with going beyond 4.5GHz he would stand a better chance with the 2600k.

hes going 50/50 for gaming and video editing. about the overclock he can do the 4.2GHz it doesnt really matter.and for the gtx 670 he decided to go with it because its almost the same with the gtx 560ti sli. Its more future proof and less expensive (gtx 560 sli > gtx 670).he was going to sli it later anyway. hes not going with the GA-Z77-DS3H but with the GA-Z77X-D3H(mistake).so he would better need to take the 3770k?

Theres no such thing as future proof in computing. He needs to get that idea out of his head.

AS far as GTX 560 SLI> GTX 670. If hes on a budget he needs to consider how much more electricity 2 560s are going to use than a single GTX 670. Normally, I don't harp about electricity usage with a computer but, When faced with a choice of whether or not to Sli 2 560 TIs or a single GTX 670, it would be folly in my opinion to even consider it. It would take an SLi 560 TIs to equal (or maybe slightly exceed) the performance of a GTX 670. But at what cost? Not only your electricty bill, but that means hes going to need a more powerful PSU, which increases the up front cost.

You only need a good quality 600 watt PSU (maybe even get away with a 500 watt) for a single GTX 670. I wouldn't touch a GTX 560 SLI setup without at least a 750 watt power supply when you're talking about overclocking the CPU too.

As far as what CPU to get, honestly, I still say the i5 3570Ks and i5-2500Ks are good enough, but thats entirely up to him.