Which CPU should I purchase? The 3820 is $30 cheaper at the moment. What do you think?
The 2600K is more expensive, but uses cheaper motherboards and RAM...
I have just bought an i7 3820 with AsRock Extreme 4 X79 motherboard, but haven't installed it yet.
I read quite a few reviews and the 3820 was slightly faster, partly due to the extra 0.2Ghz and also due to the Quad Channel RAM, but Gaming performance was pretty much the same.
If you have the funds for the better motherboards and RAM, then the 3820 will be better but they will end up about the same price.
The new Z77 motherboards for the 2600k are worth a look though.
If you are happy to over-clock the 2600k, it can get pretty fast at about 4.5Ghz, whereas the 3820 requires a different over-clocking method
so, basically after you have bought the different motherboard and ram for the X79, it will be a similar price.