Is there any reason (seat tube angle, etc.) why duplicating your ProFit-perfected BB-to-seat-to-handlebar ratio on a new bike might produce a less than optimal fit on a different frame?
Assuming all contact points are identical, of course. (Same seat, pedals, handlebars.)

As long as you have identical seat height, setback, saddle-nose to center of handlebars, etc., it doesn't matter if you have a modern geometry or 80's vintage steel right?

There are a couple factors that may affect the way the bike rides.

First, let me answer your question - if you have the saddle/bars/pedals in the exact same Holy Triangle (great term btw), you'll have the same fit.

Your bike may feel different for a number of reasons:
- wheel placement (and therefore weight distribution)
- head tube angle and fork rake
- bb height
- q factor or width of cranks or distance left/right between outside of crankarm (if this wasn't part of the Holy Triangle calculations)
- amount of shell wear/give on saddle

Of these I find q factor to really affect the way my bike fits. For me I need to adjust shoe cleat angle as the q factor changes (angle more out as the width goes up).

I remember reading an article on Gerolsteiner's team where they had problems with riders replicating positions on different bikes. They set up their own jig (which could basically set your Holy Triangle dimensions). What they found was that the same geometry frames weren't necessarily the same geometry - there were some variances between what must have been models within a line (I think they used Focus or Specialized, I forget which one).

My understanding is that if you want the bikes for the same functions -- e.g. one as a training bike, the other as a race-day-only bike -- then yes, the fit would ideally put you in the same position on both bikes.

I agree with carpe that the geometry factors will end up with a bike that feels different. If Bike #1 has a traditional frame and Bike #2 uses compact geometry, Bike #2 will be a little stiffer. Factors like wheelbase and fork dimensions will also impact the handling.

Many thanks Carp & Bacciagalupe.
My main concern is the fit.

Unless I'm mistaken, these top three factors you mention affect more the feel than the fit, right?:
- wheel placement (and therefore weight distribution)
- head tube angle and fork rake
- bb height

And for my purposes, need only to be concerned with the bottom two, in order to perfect my fit:
- q factor or width of cranks or distance left/right between outside of crankarm (if this wasn't part of the Holy Triangle calculations)
- amount of shell wear/give on saddle

I'm using identical cranks (Dura Ace 7800) across all bikes, with the exception of one with a 7803 (triple) and my mtb. Anything I can do to compensate for the extra width of the triple? I'll get another pair of shoes and shim them if I have to. And thanks for the tip (/reminder) about saddle sag--I'll start out with all fresh saddles (if I can just find one more '09 Specialized Avatar. )