Overclocking 1100T, What is the best aircooler to reach 3.8 - 4GHZ?

That will depend on how much voltage you need to get there.

The hyper 212 evo works well and may be one of the best "for the money" but if your budget is unlimited and your case is big enough, there are better ones out there.

My case is a full atx case, Ive heared that the noctua air coolers are pretty good.

This might help. (Less is better)

http://www.tomshardware.com/charts/cpu-cooler-2011/Load...

So the Xigmatek Aegir is the best option?

Out of those on the list, yes.

This test seems to have two coolers that beat it by a degree or so:
http://www.hardwaresecrets.com/article/Xigmatek-Aegir-C...

http://www.newegg.com/Product/Product.aspx?Item=N82E168...


Even on my old zalman 9900,no voltage required,just bumped up the multiplyer to 20 and sitting at 4.0ghz,completely stable.(CH IV formula and sabertooth 990FX)