I can definitely say a shallower hollow is less stress on the the legs, knees and groin especially. I tried going down to a 5/8 from my normal 3/4 I felt it in both those spots.
As far as speed goes. Yes, you get more overall speed. You do sacrifice grip in the process. It's a balancing act. Most people judge what hollow they are on by how much grip they have or don't have.
Im iffy on the more glide with a smoother cut hollow. I'm not calling total BS, just saying I don't notice a difference. I also don't notice a difference in terms of glide on softer ice.