You're doing really good at 4ghz. 4.2 is very high and you'd be lucky to see it.
As for cooling the 'next step' is a 120mm cooler for which you'll need about 165mm clearance from the top of the cpu to the side of the case or case fan if they will hit.
The hyper 212+/evo is about the best value there espically if you add a second fan in whats called a push/pull configuration. http://www.amazon.co.uk/Cooler-Master-Hyper-212-120mm/d...
Thanks for the reply.
In terms of the overclocking using AMD Overdrive I can get to 4.30 GHZ, but I'll be overheating at that point. Would I be able to make 4.3 if I spread some Arctic MX4 over it as well?
And are there any fans you would recommend? I have a CM Storm Scout with 5 fans and ideally I need the CPU fans to be pretty quiet!