held about 55-60 mph for about a minute during Hurricane George in Florida on a flat road. Race at Coconut Grove was cancelled so we went out for a ride in 50+ mph winds. 53x11, totally spun out, passed a car driving slowly on the highway. going south (against the wind) we were struggling in our bottom gear.
typical fast sprints at SUNY Purchase NY sprint workouts were 44-46 mph, very slight downgrade. slow sprints were 42 mph. there were a half dozen racers who would duke out sprints at this speed, over the course of 20-30 sprints in 2.5-3 hours.
my own sprints on Summer St typically hit 40-44 mph, 48 mph is my record. I get a leadout from either riders or a car but I sprint on my own.
In Cat 3 races the attacks are ususally in the mid 30's to 40 mph or so. The Pro/1/2/3 races I've entered sometimes average 35+ mph for a few minutes (and then I get dropped so I don't see any more of the race).