Hey Syd, don't refrain, I always use my Mark IV for practice, there is no substitute for having the "real" sound while practicing. Otherwise you are just wondering if its going to sound right when you get to the gig. I think the Mark IV with a Hot Plate works perfectly for practice, but even without the Hot Plate it still sounds like a Mark IV at bedroom levels.
I also like my 5:25 but it is a "different" sound. Good Luck!