In my opinion, the Mark Series amps have their own special tones, warm, rich, and rounded. I prefer them for cleans and leads, but for crunch I like the little bit of harshness that the rectos introduce into the equation.
I like listening to samples on Soundclick.com
Not as good as being there but better than just reading about it and having to use your imagination.
If you like what you hear, then wander over to GC and plug in for the final test. Just be sure to bring some tried-and-true settings with you so you don't give up on a great amp just because you didn't have the tweak formula.