Interesting... I never even thought of the power usage and all that. I guess I'm just used to using VMware workstation.
That set of Ivybridge is a standard power consuming processor i5 3550S(quad core) at 3.0GHZ and can be overclocked to maximum 3.7GHZ Compared to a more expensive low power i5 3317u(dual core) at 1.7GHZ that can be overclocked to 2.6GHZ. I would choose the latter any day.
This is by design in windows 8/8.1. Task manager doesn't show real cpu frequency when Hyper-V is enabled.