So this might be a dumb post but it's not a 'which bike should I buy'.

I am looking at moving to carbon from a 2005 Trek 1500 with full 105 and upgraded wheels, and have a couple of questions.

1) My shortlist is Roubaix, Defy, Synapse, but I also want to look at the Z5, 566, and RS, M1, and my first question is how do you find those non-mainstream bikes (Z5,566,RS,M1) in the right size for a test ride?? Short of driving 30-60 miles to find shops that might have your size, I'm wondering if there is any trick to finding demos. The big brands are easy enough but not sure about those smaller ones?

2) Along those same lines I would love to reuse my existing components (assuming 2005 and current 105 are similar), and just buy a frame, but even worse than above, how do you guys know what frame you want without testing it out fully equipped?

3) Are there any general differences between the felt/look/cervelo/litespeed models that are significant (i.e., one is particularly stiff or is known to absorb more road noise, etc.) and would a professional bike fit rule some of them out automatically?

Happy to hear any advice from experienced buyers.