Thank you for all your comments. RAMROD was a great adventure

To answer some questions:

My bike is an 1988 Paramount converted to fixed gear. It fits me very well - this and the contact points: WTB SST saddle, Nitto Bar, and Crank Brothers Quattro pedals make it quite easy to ride for long periods of time.

I have no problems with my knees. I don't push a big gear.

Conditioning? Ride a lot. Long rides at least once a week. Commute 56 R/T several times a month - more when I can get away with it. I also think trail running helps too, especially up hills so you get used to being stressed physically. Doing a 12 mile climb out of the saddle feels more like running up a hill than riding to me. I am lucky enough to live in a fairly rural area so all this is easy for me (the long rides, trail runs).