Depends ...what does a "Mark" sound like?
Not trying to be a smart-aleck, but there is a
huge palatte of "Mark tones" when considering a series I to a IV (never tried a V personally). And then there are the various iterations within each Mark. Not to mention with the GEQ,
any Mark can sound decidely less "Mark-ish."
I do not believe the Express can get as uber-saturated as, say, a III or IV ...it gets saturated, but not as "dense" or thick in my limited experience with a 5:50. And the Contour knobs of the Express line pale in comparison to the Marks GEQ's ability to shape tone, IMHO.
Not to say one is better ...that's in the ears of the beholder, to be sure. But if you are looking for a 5:50 to sound like a Mark (again, which one???), you can get close with some tweaking, but you will not truly be there. And FWIW, try the Crunch channel saturated ...I personally think it is a better OD tone than the Burn which sounds very exaggerated to me. Again, all IMHO.
Edward