So no heatsink, just the fan? Well, Noctua is well known for quiet fans, although some do not like the styling. Corsair just came out with a new line relatively recently and they range from quiet to powerful, I have a couple and besides a slight whirr from one of them I have no complaints (was too lazy to RMA and it has improved).
Are you over clocking? if not the stock OEM one will be fine. even with mild over clocking the stock heatsink/fan will be ok. only change it when you see CPU temp getting to high on a regular basis.
with the stock cooler 5Ghz is doable. http://www.legitreviews.com/article/1743/1/