Top tube dimensions will put you in the ballpark, but there are a few different seat tube angles out there.
This will affect setback.
Some manufacturers vary the seat tube angle for size, others, like Cervelo, doesn't. It's important to know all this because you could end up with too much setback, and it will influence the stem and post choice.
Colnagos vary their geometry between models to give very different rides for different purposes.