Actually I'm new in the sense that I haven't bought a new bike in 37 years.
I've tried 2road bikes. A 2013 Cannondale Synapse 6. The smallest size they had at the LBS was a 48. I am 5' tall with about a 26.5" inseam. His size calculator put me in a 46. He put the seat down as far as possible but the bike still didn't feel quite right in the seat area and when I pedaled, I felt like I had to give it a little extra reach on the down stroke. He thought if they shave off a little height of the seat post after I bought it, it would be fine and the next smaller, which I think was a 44 would be too small for me. I wasn't sold since it wasn't at all comfortable so headed to LBS #2 to try the Giant Avail 2 in a XS. So much more comfortable. I couldn't believe the difference. So I've pretty much decided on the Giant.
But I'm curious about how to compare the geometry of the two bikes and try to figure out why the Cannondale was so off for me. Especially when the Synapse has such a rep for being a comfortable bike. When I asked the Cannondale salesman questions about geometry, he said I was over thinking it. I agree it should come down to the test ride, but I'm still trying to understand what makes them so different. Curious if I ask them to bring in a 44 if the Cannondale would feel much better, though I hate to go down that road because I think I kinda bonded with the Giant and am close to getting it before someone else does!