Thanks for the very helpful answers!

The bike in question is a 52 cm '92 Cannondale R1000. I would guess it has fairy steep geometry, but haven't checked. I ride it on weekends, it feels good and I like the responsive, flickable feeling of a small frame, but the cockpit is not as stretched out as I'd like. It feels a bit cramped.

I have a weird body, short legs and long torso and arms. I like to ride pretty stretched out. The result of this ape-like proportion is that my daily commute bike, a 58 cm '82 Peugeot PSV, fits me well even though I can just barely stand over it. I've ridden that bike happily on back to back centuries. Actually I wish even that bike were a tad more stretched out.

In a perfect world, I'd have a 54 cm bike with the top tube of a 59 cm bike. Someday I will get a custom frame but right now I think I don't know enough about fit and my own likes to specify a frame well enough for the money I'd spend. For now, I'm thinking about how to fit that C'dale better.

I will do the A-B comparisons mentioned.