Well long story short I test road a Caad9 and a Synapse. I liked the ride on both. I have a really old/vintage road bike late 80's maybe that I've been riding that is far to big for me . To be brief my inseam is 29.5-30" (74.9-76.2cm) and I'm 5'6". I know I'm not going to get a pro-fit from the feedback I'm just trying to educate myself as to which frame geometry measurements are most important.

I took some measurements as best I could of the current bike I'm riding and am trying to compared frame geometry of the Caad9 , Synapse and the current bike. One dimension in question is the Stand Over Height. As I am on the shorter side it seems that I will not clear the stand over height on any of these frames.

Stand Over Height
Caad9 (50cm) = 74
Synapse (51cm) = 74.4
Caad9 (52cm) = 76.5
Synapse (54cm) = 77.1
Caad9 (54cm) = 78.5
Current Bike = 81.3

The Caad9 (50cm) and the Synapse (51cm) are the only two that I will actually clear buy 0.5-1.0cm.

But then looking at other dimensions as far as TT length they seem to be on the small side compared to the current bike I'm on and I actually feel ok on it. Although I have noticed on rides ~15mi I get numbness in my left foot outer toes and I think that is entirely related to saddle, saddle position, and Seat Tube length which there isn't much I can do about on this old frame.

TT Lengths
Caad9 (50cm) = 52.5
Synapse (51cm) = 52.5
Caad9 (52cm) = 53.5
Synapse (54cm) = 54
Caad9 (54cm) = 54.5
Current bike = 54.6

I actually feel ok well at least I think I do with my current bike.

Measured Size (BB – TT, measured from Center Line of BB to top of Tob Tube)
Synapse (51cm) = 45
Caad9 (50cm) = 48
Synapse (54cm) = 48
Caad9 (52cm) = 50
Caad9 (54cm) = 52
Current bike = 58.4

My current bike has virtually now seat post exposed. The issue I have with the 54cm frames is that there is only about 1.8-4cm of seat post exposed. Just seems like the 54cm would be to big of a bike for me. Yet the on-line fit calc suggests a 54cm to be the right size for me.

I could list every and all dimensions instead I made a spreadsheet with them. Would anyone care to comment on them and help me out. Am I looking at the correct dimensions to decide on the best geometry for me?? or should I be looking elsewhere to establish a baseline geometry for me?

Then there's the question of do I go with the Caad9 or the Synapse ?

Thanks in advance