Originally Posted by
repechage
At least they are in the same size range.
map out what are the requirements. Geometry musts. Tire size preferences. Assuming 700c or tubulars.
Who will be doing the assembly?
in general, a complete bike will be less expensive. Purchase, adjust to fit as needed, adapt to it and note how the handling differs from what you otherwise have or recall.
a whole bike will provide answers quickly, then move to the next with some basis of comparison.
As. professional systems engineer, I think mapping out requirements can become way too complex, though I try to do it. But I have near 60 years experience, and repechage (I imagine) more, certainly in most aspects. I’ve recently bought a Mercian King of Mercia, about 1975, long and graceful. My concerns were size/fit, clearances for my intended gearings (Campy 2 or 3 in front and 8 through 11 in back with caliper brakes), and fender eyelets. Now maybe that’s all the requirements definition that I need, but it’s my experience that lets me make these choices very quickly,
To the Thread Starter, I learned not by starting with frames, but with bicycles that I liked. I would think about how to recognize when a bike is like that well-loved old one. Buy that example as new as you can, and use friends, books, people like us, and online resources (Lennard Zinn, RJ the Bike Guy, or a repair class in a Community Education program local to you) to set up, adjust, fine tune, and maintain that complete bicycle.
This way you get to discover, ride, learn and see more of the world sooner, spending only the minimum on bike shop labor fees.
Also I don’t know if it’s available, but the websites by an old-timer here, Randy Jawa, addressed these matters brilliantly, if you can find them.
How old would your ideal road bike be? In the early 1970s there were a lot of pretty good-riding bikes from Italy, notably Atala, Fiorelli, Bianchi, and Bottecchia, I suggest these over French bikes because of the concerns over French threaded parts. but these are all friction shifted bikes.