The highest recommended system RAM I've seen for a game is 4GB for BF3 which isn't even out yet.
You're getting 4x as much RAM as one of the most system intensive games that's going to be released this year.
Diablo 3 beta recommends 2GB, so thats 8x the RAM for that. You're spending $ on something you'll never utilize.
I haven't overclocked the 2500K yet, but from all accounts I've read it isn't too difficult.
The CPU and motherboard you're getting are very popular, I'm sure it won't be hard to find a guide online to do it.
Heat is the OC killer, as long as you have adequate cooling and don't push it beyond what it can handle temp wise its fine.
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There really isn't any reason not to get the K version, its only $10 more, or $10 less if you get the combo.
Even if you don't overclock it that fact that you can will increase the resale value later down the road if you want to sell your machine.
*Edit - Also, you need thermal paste if you're applying an aftermarket cooler Tuniq TX-2
or Tuniq TX-4
. Reviews say theres a 3-4°c difference between them.