Case fans and CPU coolers will do sod all for mosfet cooling (with the possible exception of top-down cooling but that won't do much without actual mosfet heatsinks).
To clear up any confusion, the mosfets are these bits:
If they're not properly cooled (as above) it's a recipie for disaster with high-end CPUs.
The one edit I might recommend is that if you fancy having 6 CPU cores rather than 4 there's a 3.3Ghz hexacore model of that chip for £20 more:
http://www.scan.co.uk/products/15-cashback-amd-fx-6100-black-edition-orochi-core-s-am3plus-33ghz-12mb-total-cache-ht-5200mt-s-95w-rAlso you should probably switch to a different hard drive, western digital (particularly the caviar blue/black series) are generally better hard drives than these hitachis, I really just put it in there because it was cheap for what hard drives seem to cost at the minute...
Not really on this kind of budget.
If he was spending £1000, or even £750, then sure, go i5 2500k, I make a stupid number of machines with those chips and they perform very well. But you can't make a decent 2500k build for less than £700, and the AMD chips still perform admirably. The only modern applications that require really mega per-thread CPU performance (ie, applications in which the intel chip would be noticeably better) are in high-end simulation...
And on applications which can spread the CPU load around many cores, the AMD chips punch above their weight price-wise.
Also there will be no more new 1155 or 1156 socket performance chips, whereas AMD's platforms generally provide upgradability.