i5 2500K @ 4GHz with stock cooler?

[moezb]

Yeah, I noticed that after I tried running Prime95

 

[moezb]

LOL yeah, I realized that after actually looking up the parts. When I searched TX2 on TigerDirect, it opened the page for the TX3 CPU cooler, so I just assumed it was a newer version. Does the paste really matter? Shouldn't the one that comes with the cooler be okay?

 

[Chaos Residue]

Should they be? Of course. Are they? That's up for debate. When it comes to thousands of dollars of computer parts it's better to be safe than sorry. That's my outlook anyways. Arctic Silver 5 is the most widely known for being a great thermal paste. There are lots of others to choose from, but which one to choose is up to you.

 

[Roark]

Does the paste really matter? Shouldn't the one that comes with the cooler be okay?

There is generally a few degrees difference between aftermarket pastes.
Considering the overclock you're looking at you'll be fine with the stuff that comes with the cooler, if you want to drop ~3°c then go for something else like TX-2/MX-4/AS5.