@knups I have i5 4690k at 4.8ghz and it will run game at 144+ fps. I put the frame limiter to 144 because I was getting the same kind of hitching as you and it helped. I still get the stuttering but no longer game breakingly bad. Also your cpu should get to 4.5-4.6 easily with slight overclock (obviously with decent cooling).
I used to have gtx 980ti and upgrade made virtually no diff on low graphics settings.
Summer ambient temps can cause crashes when running fine before on lower ambient temps. My game started crashing due to this and I had to lower cpu overclock to get it stable again. Maybe something to consider if you run an overclock and already tried reinstall and config files delete.
I get that NWI did this to try to slow the game down, to prevent sandstorm becoming too much of a twitch shooter, with both the free aim sensitivity reduction along with the free aim crosshair to ADS crosshair misalignment as obstacles to muscle memory flick shots.
Unfortunately the sensitivity reduced 'sticky centre' just makes the game feel bad. It just feels like input lag. I think it also balances the gameplay too much in favor of the defensive side, it disadvantages movement too much. On open maps with so much clutter and so many places to get shot from, a gameplay mechanic which hinders your ability to quickily scan your surroundings makes movement too risky. In my opinion the free aim sensitivity needs to be much closer to normal panning sensitivity.