You don't say what size range of fifth wheel you are considering... 28ft, 42ft, or something in between? We full-time in a Grand Design Reflection 337RLS (36', 14,000 lbs. GVWR). I'm 5'11" and have never felt claustrophobic in the rig (and I tend to get that way in small spaces). The RV has the typical higher roof at the front tapering off toward the rear. This is to accommodate the bedroom and bathroom what are elevated by three steps above the main living area. I have full walk-around headroom in the bedroom and bathroom and have to stand on tip-toes to touch the ceiling in most of the living area. We have spent time snowed in and times when the 100 degree temps limit our outside time without feeling confined. I'm wondering what you're worried about.
Rob