I am building a Gaming PC (SLI capability is a necessity) and would like advice on what kind of MoBo is necessary for a stable 5Ghz+ OC on the Core i5-2500K. My current pick is the Asus P8P67 EVO ($200). Should I upgrade/downgrade? Are there any features that I am missing/don't need?
5Ghz is quite high for a 2500k for day to day operation. You'll have to get lucky with a good chip to be able to hit that speed without needing a voltage level that will reduce the lifespan of your chip to only a few months. (Not to mention some serious cooling)
Most 5Ghz+ speeds for 2500k/2600k's are just for short term benchmarking, not running constantly. I believe one of the few I've seen that was for daily use actually used an open 100qt cooler with gallons of ice suspended in it to keep the temperature of the water under 10c, and was running at over 1.5v! (1.35 is a good top voltage to shoot for daily if you want your CPU to last years)
With as much as you'll have to spend on cooling anyways, you might want to go with the 2600k just for better binning that will hopefully let you use a little less voltage though.
As for the motherboard, it's a good board that shouldn't hinder you, but I think people generally use boards like the Sabertooth for 5Ghz+.
Is there a reason you need to hit 5Ghz? 4.6 is plenty for all games and will be much easier of your components.
After reading your responses, I have concluded that 5Ghz is too high for daily use, and I should be shooting for something much lower than that. My previous plan was to buy the Corsair H60 + Arctic Silver Thermal Paste & Thermal Paste Remover (to remove the paste that is pre-applied to the H60 - total of $92) with the Core i5-2500K. If I am to go with the Core i7-2600K (with 1.35v goal) as suggested, what heatsink would you recommend? I will need to spend far less money on a heatsink if I am going to spend $95 more on the CPU. Also, what kind of clocks can I expect from a 1.35v OC?
You can stick with the 2500k no problem if you dial your overclock expectations back. It's a great CPU still, it was only if you insisted on trying for 5Ghz that you really needed the 2600k for the best shot. You probably see in the range of 4.4Ghz at 1.35v depending on the chip you get. (4.2 if you get unlucky. 4.6 if you get lucky)
You can also get a quality air cooler that's just as good as the into level H50/60 corsair water coolers for less $ unless you really want water. There are a couple good sites that compare CPU coolers you can find pretty easy on google. (I'd link u them but I'm posting from my phone)
Your new plan sounds much better though, you'll never notice the difference in games, and it will be a lot easier to get working, and keep working for years.