You could probably sli 2 GTX 680's on a good 750watt, so yeah, that 850 is a lot more than you would need; if you are not planning on sli, than a 550watt will do fine. Just make sure it is a good one, like Antec, Corsair or Seasonic. Where are you located, anywhere near a Micro Center? They always have deals on i-series processors and good z68 chipset motherboards when bundled together.
The ASRock is a good board or the ASUS P8Z68-V gen/3 is another good board, slightly more but still less than $200, and should be compatible with Ivy Bridge processors with the right BIOS, for possible future upgrading on the same board. However, if you get a 2500K that should be all you need for a few years.