I once hit 39mph on a town line sprint on flat ground, no wind. Massive tunnel vision, saw stars. Not sure how I did it, couldn't repeat it. I got close a few times, at 37, even 38, but never quite got it up there on subsequent tries. I quite literally think that it hurt so much on that one effort, I simply mentally could not push myself to get that extra giddy up again. I seriously never really bothered much with sprinting in the ensuing years after I did that. Not sure why, guess no need to really. Other times I've done all out sprints were at steeper angles or on downhilly-ish roads, so probably don't much count. I'm proud of that effort, but again, it hurt like nothing else. And I don't think I was even in terrific shape at the time, but I was sprinting a lot.
Regarding 'recreational fast'....I've noted amongst my peers in the clubs and such, that speeds of 18 or 19mph were the common 'recreational' fast up until GPS devices and social media started making it known exactly how fast people were riding. It was rare for us to average much more than 19+ on group rides, regardless of how flat or far the route was. Now? Some of the group rides are so fast, even for me, I don't bother to show up, because I'll get dropped on our way to a 22mph average. This can be some 35miles over 2,500 ft of climbing, and still average that. It's not just racers, but a lot of club riders. Things have simply gotten faster. It's made it rather hard in the last year or two to 'be' in shape enough to do some of these rides. The time commitment has also stepped up along with that. Used to be, you could get away with maybe riding 3 or 4 days a week, now, you have to be riding pretty much 5 or 6 days out of the week. It's INSANE.
And I cannot begin to tell you how much the above sucks for me this summer. I've just not had the time to get in the miles. Despite a lot of these rides being 'no-drop', you still find yourself lagging far behind, really struggling to keep the pace, and so I've declined invites on numerous occasions.