A question that comes up over & over. Yes, size matters. You will find that most of those who say no problem with at upper 30s 5er are people who use the commercial CGs mostly.
State parks &, even more so, National Parks can be extremely limiting in sites the larger you go. Some states are better than others. Presumably you are buying for travelling the country not just the local weekend place.
What does the 37'er have that a 34'er does not have besides more floor space?
I did the research on the SPs & NPs first. We were buying for extended travelling & wanted to get into SPs & NPs with few problems with site size. The target max length was 35'. We finished with just under 36' LOA. Over 1500 nights on the road in 10 years & we are sure glad that we stuck, almost, to the length.
Boat: 32' 1996 Albin 32+2, single Cummins 315hp
40+ night per year overnighter
2007 Alpenlite 34RLR
2006 Chevy 3500 LT, CC,LB 6.6L Diesel
Ham Radio: VP9KL, IRLP node 7995