For what it's worth, I'm in the process of selling my Sennheiser HD600s, and one of my friends already sold his HD600s. The HD600 is supposed to be one of the better values in headphones, and retails for $100 more. However, I find the bass quality and detail level to be superior on the Mad Dogs. Other than that, they're fairly similar from a sound perspective.
Doing the same... WE ARE GOING TO HAVE A PRICE WAR SOON!!!! LOL!