As I said, I5 CPUs do not have hyperthreading.

Anyway, hyperthreading is only used by very few games and might not be worth your money to get an I7 just for it (depending on what you're planning to do with it of course).

MikeWW and yotusffy explained very well everything you need to know about cores and threads, I would sugggest you to get an I5 6600k if you can afford it and really want to change now. Otherwise waiting for the next generation seems to be the best idea (Amd Zen and Intel Kaby lake)

Edit : typo