I am a little over 6'4". We have a 2007 Montana. I can walk straight upright until I get half way across the bedroom going toward the front of the trailer. But the only time I go farther is going to bed anyway. Newer models have more headroom.
But the only way to know for sure is to visit dealers or shows with models of interest and walk thru them. I remember walking thru one 5er (don't remember brand) at an RV show that seemed to have lots of headroom in the bedroom. But they had placed the TV antenna handle right where you walk. Had to duck to get around it.