Honestly, neither. Hyperthreading only affects a select few games and is miniscule. If I were you I would go with a i5 4690k, it will definitely last 5 years. Don't listen to the people that say games will be use more cores soon. They've been saying that for years. I have a friend with a i5 2500k and it can play all the newest games with ease, albeit with a good GPU to boot. So if I were you id save your money and invest into a better GPU down the road like a GTX 980.
EDIT: Didn't see that post just now where you mentioned the SLI 970's. With those two GPU's and a i5 4690k you'll be set for atleast 5-7 years.