I have a 990x overxlocked to 4.4ghz, and it is still about 2000cb in r20 multi core. The 11400f with default power limits on place is ~3300cb, ~3800 without. That is certainly significant, and the difference between something like a Xeon x5680 will be be even larger, probably with the Xeon delivering half the performance of the 11400.
BUT, you can get an X5680 (Identical to i7 980x) for $35, on eBay, which is (not joking) 10 times cheaper than an 11400+b560 board+16gb ddr4.
Up to the op, but I personally would at least try the Xeon/i7 before spending so much on a new everything.