Try upping your res if your on 1080, say 2560x1440 using DSR. This might increase the gpu usage a bit and take some work of the CPU. Bf4 is one of the few games that really benefits from an i7 with sli.
Tried this and made it run at a much lower fps.. Wasn't nice to play at all.. I only play rush 32ppl.
What frame rates are you getting ? On a 970 SLI rig, it should be well over 100 FPS in 1080p gaming. At this rate, unless you have a 120 Hz monitor, you won't see differences by going to an i7. Even if you do, anything above 60 FPS is more than acceptable.
It's over 115fps on open maps, but say pearl market on rush it goes down to 50-70fps if a lot is happening and isn't smooth to aim