So per Scott's "DAWBENCH" numbers at resonable air cooling overclocks of both the 2600K and 3820 you are looking at around a 10% performance difference (number of RCX compressors / 261 vs. 290 / *the 290 just isn't in his charts yet) and additional cost of around $70 for CPU/motherboard plus whatever your video card costs. I seem to remember Scott saying something about the X79 platform being pickier about what ram you used so that might be something to be aware of with your build.
One last thing for others reading this thread is that when overclocking it's still "luck of the draw" with what a CPU will overclock to and that alone could be a 5% difference in CPU performance. For me personally I would choose the 2600K/Z77 route for price and probably shoot for a stable 4.9 Ghz overclock (Scott's test numbers were on a 2600K at 4.7 Ghz) which would level the field a bit more. If you have a Microcenter nearby they ran a sale that was sold out in a day where they had the 2600K for $200 and if you bought a motherboard along with it the motherboard was an additional $50 off (WOW another $110 savings from the figures we were talking about in this thread). Too bad I missed it but who knows, they may do it again. Just something to keep your eyes open for.