We have this conversation during a lot of our rides. One of our best climbers says he gets sketched out in the mid 30s. Our bigger guys will regularly do 40+ on decents. As a former big guy, I never had to worry about working that hard on downhills and have hit 50.4 according to my garmin. Now that I'm a bit thinner, I can't seem to even break into the high 40s on decents I've come close to 50mph before. Maybe it's a bit delusional, but I don't really worry about wiping out at 50mph any more than I do at 30mph. Either way, I'm going to be hamburger. It's pretty much luck of the draw how badly the crash is going to end.