I did this as part of a 7 day trip around parts of Europe. It was by no means intentional, we thought it would be around 70miles, but clocked in at 106. I did it on a hybrid - specialized sirrus with a carbon forks etc, so pretty close to race bike spec, but with flat handlebars. Also had a weeks worth of gear in the panniers, and was riding up and down hills. We actually cycled in belgium, luxembourg and germany all in the same day. The whole jaunt took around 10 hours, but we weren't racing, stopped for a good long lunch, and got lost once or twice.
Doing it on a single speed would certainly be interesting. I haven't had enough experience to give a definite answer, but if you are fit enough and the bike is comfortable enough, why not?