Your choice in case is going to decide everything. Most of the m-itx HTPC cases are not gonna allow you anything much bigger than a stock heatsink/fan. On the other hand something like the Coolermaster 360 gives you alot of room for aftermarket fans. The bigger the fan the more air it moves at a lower rpm and usually the quiter it is. You can fit a h50 closed loop in a Coolermaster 360 also any heatsink under 110 mm or 4.5 inches should also fit in the case.