Well it really depends what games you will play on your rig, if you're looking forward to play ESL title games, then sure, but if you're looking up to play few years ahead with the pc you're building, then if i were in your place, i would invest those extra £40 (in uk) for 6600k which you can overclock incase next gen games are more cpu intensive than current.
Ofcourse 6500 comes with stock cooler and for 6600k you will need aftermarket cooler to actually overclock it. but that's something to keep in mind. either way, i think it doesn't matter what cpu you have got, never go with stock intel cooler, its just rubbish.