My two cents... as a musician, and a person very sensitive to sound, especially monotonous road noise:
I think the XL is plenty quite. In fact, when I was in the "looking" phase, I noticed no difference between the road noise. I have not driven an H. Only XL and XLII.
As for the length... I don't see why somebody would prefer a 40' over a 45'. I wouldn't NOT purchase a 40' if I really like the bus, but if give a choice, I'd go with the 45' every time.
And hey, I like the way the rivets look. These busses have enough issues without panels randomly coming unglued and falling off :-). But really, rivets just look cooler. I don't think anybody would disagree with that
~Adam