Just a few thoughts. First, you really need to have realistic expectations. You can't just say you want Ultra requirement performance, but you're only willing to pay $600-$700. If you want the best, you have to pay for the best. Honestly, the rig you have in the OP isn't that bad. And just for your info, the 970 isn't going to be a huge leap over the 780. In some benchmarks, the 780 still does significantly better than the 970, but in others, then 970 barely squeaks ahead. It's not really going to be worth the money to buy a 970 over the 780, and I know some people who swear by their 780s that they're getting 4K performance. If you're going to upgrade your video card, you need to either wait for the next generation to come out in a couple of months, or go with at least a 980, which is going to blow through most of your budget right off the bat.
We can put you together a part list for the CPU, motherboard, and RAM if you want, but it's probably not going to make a huge difference until you upgrade the GPU. Anyway, if that's what you want, I would recommend going with Skylake and DDR4 RAM. So if that's what you're after, here you go:
Intel Core i7-6700K - System Build - PCPartPicker
It's an i7-6700K, a good Z170 board that supports overclocking and SLI, a Hyper 212 EVO cooler, and 16GB of DDR4 RAM for $539. If you need a case and PSU, you can add it in for more money. Your friend would definitely be better off going with an i5-6600K and putting the extra cash towards a better GPU. You would probably be ok with your 780 until you're ready to lay down $600 or so on a better GPU. I'm not guaranteeing what the performance will be on your specific game, but that's what you asked for.
About the i7 vs the i5, I actually think it's a waste of money to go with the i7 if you're only gaming, at least until we get more DX12 multicore support. Personally, I would only spend the extra cash on the i7 if I were going to be doing things like CAD or video/music editing. Either that, or if you're just in a pissing contest.