We use the 212 exclusively getting up to 4.7-4.8GHz at 75-85 Deg. Thou if you're a gamer you'll never see above 55. Xigmatek makes a nice cooler also but I believe it's roughly $20 more.
Yes IB runs hotter than SB, but it's made too. Due in part to it's smaller architecture. Yes you will see benchmarking increases from 4.2 to 4.5 but it would hardly be noticable to the naked eye.
IB can do 4.2 very easy without even changing the voltage. 4.5-4.7 is optimal. Thou your biggest performance gain would come from GPU not your CPU. Depending on your application ofcourse.