you will see no performance difference if you upgrade to i5 and stay with gtx 960 .
on the other hand if you change your video card for gtx 970 you will see a huge performance increase
(but there is no point to buy brand new gtx 970 at this moment , used for 200 or 220 might be a good idea ,
otherwise rx 480 which will be available in less than 10 days will be much better choice)