There really isn't much point, only a 20-30% increase if you buy the latest and greatest. You have a top-performing CPU already. If you haven't overclocked it you can easily match the performance of any of the non-overclocking i7s.
I upgraded from an i7-950 @ 3.85Ghz to an i7-4770k @ 4.3Ghz, not much noticeable difference in most things. I wanted the intel SATA III controller for my SSDs versus the intel SATA II on my X58 board (the two port marvell SATAIII showed less performance per channel when two drives were hooked up)
Might be worth it to wait for Broadwell, or the chip after that in 2015 which will have yet another new socket.