Not necessary for 4.1Ghz. You could do that with the stock cooler.
3.5Ghz-3.9Ghz already, so you would only be adding 200Mhz. All the way up to 4.3-4.4Ghz I would say stick with air cooling. Everyone's favorite Cooler Master Hyper Evo 212 can do that quite easily. Also plenty of other coolers in the 25-35 pound range.
With a high end cooler like the rajintek or an h100i ,and decent luck with the CPU, you could hit 4.6-4.8Ghz quite easily.
Hmm.. I just had a look at that air cooler, the aesthetics bug me quite a lot...
But strickly speaking, does that rajintek seem a good like a decent component?
I have this water kit on my setup, it is very good, idle is 12-16 and on TERA ultra is 39-43 depending on how warm my room is, I have overclocked to 4.2GHz, you can get this for the looks if you don't really need it, but its better going with the artic freezer 7 coolers for stock Speeds.