I'm a fairly massive guy with many miles in my legs. I'm naturally strong and naturally larger. Rugby was my best sport. I run 2-3 days a week. I am pretty fit and pretty overweight if you believe both exist. The local group rides near my house are often 26-30mph. It is when the train overpass is 28+ I get dropped. On flat holding 30 in the group is NP. Solo, on flat 21+ is easy. 1% grade - not so much. Flat is not so common around here. As I'm never really in a hurry to go anywhere I responded in the 2nd group of the <21mph. I ride a couple time a year with an 82 year old that does 21+ all ride. Big John Watkins broke a lot of riders legs in the day. He rides about 80 RPM and it looks lie he is soft pedaling, but he's not.