I have an older (not MKII) MK50H so I can't really comment on the MKII but I really like the one I have. IMO, mine doesn't do the higher end of it's gain spectrum as well. Loses tightness. But at rodded JCM800 levels and below it's excellent. I think of it as a cross between SLO and XTC...somewhere in that neighborhood...kind of. Has a great feel to it too.
And FWIW (again I'm not familiar with the MKII), I like it with the Volume (aka Gain) control high and the Overdrive control at low levels. At that setting, switching to Overdrive still has tightness but it's only a slight gain boost. Just the Normal channel with Volume (Gain) at high levels it is at rodded JCM800 levels of gain.