If it's only a $10 difference, it would likely be worth going with the 7700k, since it comes clocked higher, even if you aren't planning on overclocking. The only downside would be that the K processors don't come with a stock cooler, but the Intel Stock coolers aren't particularly good anyway.
Do note that Intel will be launching their new 8000-series Coffee Lake processors within the next two weeks though, and those will feature 6 cores on the i5 and i7 parts, so it might be worth waiting a bit to see how those fare.