At what point do I need an aftermarket cooler? (3570K)

Gents,

Pardon me for asking what are probably stupid questions- I'm a complete newbie at buildling comptuers. I'm currently working on my first gaming desktop, still in the purchasing phase.

I am wondering if I need to add a cooler? I have read that the i5-3570K stock cooler is decent enough for a stock cooler, and the case I've purchased (HAF-922 from Coolermaster) seems to be well suited to keeping the inside cool.

I am running a:
i5-3750K
ASRock Z77 Extreme 4 MoBo
And I'm still deciding on a GPU (trying to pick one from 7850/7870/660/660 Ti)
Inside the aforementioned HAF-922

I am planning on OC'ing slowly, I will probably start around 3.8 and move up to 4.0, and increase as I need it down the road.

My first question is will the stock fan be sufficient in that setup?

Second, as I increase the OC, at what temperature should I be worried and definitely buy an AM cooler?

Third (and this may be a very stupid question), is running without the side panels on the HAF-922 a terrible idea? I realize more dust can get in, but the sides are vented already. My tower will be sitting near a fan that has an air filter in it (I have allergies), so I can actually set it up so that it moves air through the case from the sides. It seems like this would provide a lot of extra cooling, so does that outweigh the problem of potential extra dust? Also, noise isn't really a factor, as I game with headphones on.


I'm not necessarily trying to take the "cheap" way out, as I know that good coolers are only ~$40, but at the same time if they aren't necessary, that's also about the price difference in upgrading from a 7850 to a 660Ti, so I want to put it where it's most beneficial.


Thanks All!