On the 8 core I always see the CPU speed up at 3,4ghz, rarely ever above, sometimes 3,5 because so many tools I use utilize all of the cores. Cool thing is that the boost is active almost all the time. And the nMP never ramps up the fan or has too spin the turbo down due to heat issues.
The iMac can keep it up for a 20 minute render too, but man it gets loud!!
My single core geek bench score is about the same as on my old maxed out late 2012 iMac (which boosted up to 3,7ghz) though. Plus minus 10 points.
Multicore flies though! After effects renders a comp that previously took 24 minutes in 13 now!!!