Not worth updating from a 2500k. It does everything a 3570k or 4670k can do, and has a better cooling interface allowing for better temps overclocks. Hyperthreading isn't going to make or break any game at this moment. There won't be any discernible difference while gaming going from a 2500k @ 4.4 GHz to a 4770k at 4+ GHz.
4.4 GHz is plenty to feed a crossfire setup. I averaged 70% usage on an i7 3820 (think the 2600k's more well-connected brother with more memory bandwidth and PCI-E lanes) in BF4 with 2 GTX 670s. I just game with 1 GTX 670 now as I've put the second one in another PC.
The only better thing in this case would be a 6 core like the 3930k, 4930k, etc... but that would require a new motherboard with the x79 chipset and possibly another couple of ram sticks to benefit from quad channel memory.
I'd advise you hold steady and put your money towards 290x cards when they drop in price after the coin-whoring bubble pops, or towards big Maxwell later this year. Your CPU is more than adequate for the time being, but more GPU power will definitely make a big difference.
i7 3820 @ 4.4, Custom Water Loop | ASRock X79 Extreme4 | 8GB G.Skill 1638mhz
GTX 970 @ 1465 | BenQ 24" 120Hz | Samsung 840 250GB | 2x2TB Toshiba | Win 8.1 Pro x64
X-Fi Titanium Fatal1ty Pro | Sennheiser HD555 | Corsair TX850V2 | Fractal Arc Midi R2