Your Corsair TX850 is more than enough PSU to power your two EVGA GeForce GTX 670 Superclocked GPUs in SLI. The GTX 600 Series from NVIDIA is one of their most power-efficient designs, and the Corsair brand is very powerful.
Both of the GPUs would barely push over 250W per card, even under extreme load - and the rest of your system should be fine, even with the overclocked Core i7 2600K. If you were to be talking about tri-SLI, then you might run into some troubles with the PSU - but two-way SLI will be absolutely fine.
That's a nice system you have there, with those EVGA cards!