I like this thread.

The OP has more distance experience than probably anyone I've seen posting in the SSFG forum, so I have real doubts about anyone here being able to give you helpful advice. But good on ya for what you've done so far and what you have planned.

I'm ~40 lbs overweight right now, so I'm slow everywhere and wheeze a lot up hills - last year I did my first century on a hybrid set up for touring. I'm confident that I could do an easy century without too much climbing on my fixie if it was just about the legs, but it's also set up with much more aggressive ergos and the rest of my bod couldn't handle it. I would like to do a 100km ride before too long, though - even if it would take a few days for my wrists, shoulders, and ass to recover.