Best thing I can say about the i5-2500K is that it's adequate for stock settings. And I don't remember the noise being a concern (been a couple weeks now since I last used it).

That said, I'd still use the Cooler Master heatsink. It'd be more hassle to return it. NewEgg will charge a 15% restocking fee (about $5) and it'll probably cost about $10-12 to ship it back. You'd be getting less than half your money back.

I'd remove the side fan and put it in the bottom of the case.

Have the front and bottom fans blowing in.
Have the rear and top fans blowing out.

If you want a side fan, maybe these thin 120mm fans will fit.
http://www.frozencpu.com/cat/l3/g36/c15/s972/list/p1/Fans-12_Volt_Fans-120mm_x_12mm_Fans-Page1.html
Normal fans are 25mm thick, these are only 12mm thick, so less than half the thickness.

I bought 2 for the 2 computers I built for me and my wife. I don't even NEED the side fans. The Coolermaster comes very highly rated. 2400-ish reviews on Newegg and it's rated 5/5 eggs.

 

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I'm serial. That Hyper 212 is going to be more than you'll ever need running that i5 stock.

It makes that side fan irrelevant, if you are not overclocking. Even when you DO overclock later, the side fan may still be irrelevant.

And trust me, it's a helluva lot easier to mount when the mobo is outside the case. As well as allowing you to see if you are gonna have any clearance problems with memory (don't get the highrise kind with heatspreaders) or chipset heatsinks since every mobo layout is slightly different.

I've used the Hyper 212 on both of my last CPU builds. Just built a new one last week with an i5 2500k just like you. I'm stock and this thing runs at 40 C full load (prime95), about 24 C under normal status. Couldn't fit a side fan on my case, and frankly with those numbers I'd say I'm not missing it.

OC later, I'll see how it goes. But unless I get really high temps then, I'm probably not going to worry about that missing side fan. There is always the option of tracking down a slim fan (Scythex makes the only ones I've ever seen, 12mm), or if you don't care about aesthetics you can rig the fan up to the outside of the mesh, using zip ties or thin metal (like twistie ties from your bread bag).

Don't overthink this. Ravyn is correct, you are going to lose your azz if you send that cooler back to Newegg with their ridiculous restock fees and (them) not picking up the shipping (10+ for you....). And later, you'll be kicking yourself for not using the Hyper 212 anyways. It's one of the best bang for your buck air coolers you're going to find.

 

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