For ME personally, ill use the threads as I edit pictures and video and threads help to speed up exports. However, if you're just gaming only, I see no need to spend extra money on a feature you'll never use. Between a 9600k and an 8700k, i PERSONALLY would take the 8700k simply because it does hyperthread to 12 threads. (9600k doesn't support HT) Single core performance and the price is around the same (depending on where you get it) If you're up for it too, you can OC the 8700k. For gaming only, get the 9600k since you won't use the threads
TL;DR:
Gaming only: won't use the threads, so get a 9600k, save ~~$80. Gaming uses 1 core usually, HT will have no effect
Gaming/working on multithreaded stuff: get a 8700k. Spend ~~$80 for HT, which you WILL use for multithreaded stuff