Turbo boost has to do with threads more so than cooling. If you have a task that is single threaded the processor will use higher multipliers to make up for the fact that the remaining normally active cores can't be used. This is a defacto "heat" thing as less cores are used, more thermal headroom is available for the overclock. If the 2.7GHz i7 does not upclock in the face of single threaded apps than something is up but doing a single processor bench with Cinebench could tell you in the results if you compare. My guess is it is working fine as all other Intel chips in Macs are not crippled.