Extreme RC posted a very good article here testing inrunners versus outrunners.  The test motors were ARC, Medusa, Hoffman Magnetics Beast, and Jet Screamer.  The inrunners delivered significantly more thrust per amp consumed and the ARC was slightly more efficient than the Medusa.  I was quite disappointed with what I saw on the Jet Screamer and the Hoffman Magnetics motors, especially given all the hype on some of the forums. 

If I find the thread again, I'll post the link.

Rob