I had a shop modify my single speed in imitation of bikes like the three speed Raleigh Record Ace. As tcs says, coming from a single speed to three speeds is a revelation. I don’t mind the wide gaps because I was already used to varying my cadence.

I’ve done 40 miles on it at this year’s Five Boro Bike Tour. I’m sure I can do a century on it as long as the hills aren’t really steep and really long.