Had the same dilemma myself a few months back while deciding which way to go with my current rig.
If you use, or plan to use software other than games that benefit from HT OR you do a lot of video encoding the i7 is the better choice.
If you only intend to game or do little video work (like me) the i5 750 has similar performance and is a deal cheaper.
Me, I could not justify the extra expense of an i7 setup, but the choice is yours to make.
BTW, that cooler is one of the better 'cheap' ones it keeps my CPU below 70C at just 50% speed and 3.4GHz under Linpac loading although your ambient temperatures might be higher than those here in England