You will not notice the difference, especially if you run higher game quality settings and a resolution higher than 1080p. However, since the i5 7600K has a 200Hz higher four core clock speed than the i7 7700, it would be a few frames faster.
Unless you use your PC for productivity applications like video editing, you will be better off with the i5 and save money or put it into a better video card or some other hardware component. There are only a handful of games that utilize an i7's four extra virtual cores and many actually run worse on the i7 with the hyper-threaded cores. Here's an old GTA IV example of that:
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