Both CPUs are great.
And with the right MB You can OC even the i5 6500 and while benchmarking the OCed 6500 beated even i7 6700k not OCed. But OCing non K CPUs has some downsides so if you are not budget limited I'd go for 6600k over 6500. Or! If you really do not want to OC you can pick i7 6700 non-K that is absolutely fine with stock cooler w/o OC. So that might be the option for you.
Also wait for AMD cards. Maybe they will be better, maybe not or maybe just the same performance. Either way the prices will drop as Nvidia is utterly overpriced right now due to no competition. Of course RX480 is not a direct competitor to GTX 10XX series but it should still perform similiar to GTX 980 for half the price and that is more than enuff for 1080p gaming. So IMHO wait till october when Vega might come to see what card is better or how the prices will drop.
Cheers!