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.