Originally Posted by
derekfulmer
Thanks. I'm also comparing my old Allez geometry. I really think the 61 would be too large.
I wouldn't put your Allez's geometry in the mix at all. Very different bike. Maybe if it were a Secteur (endurance), but the Allez is going to be too much of a jump in what kind of bike you're looking for. For sizing solely, only look at the stack, reach, and effective top tube. And consider the CX bike will probably have a slightly shorter reach + higher stack due to the rider position it's intended for.
Ideally, take it for a ride before buying. Sorry, online buying is a risk on fitting because there's no industry standard on measuring frames. Different brands have different tolerances and reference points on where they actually base their top tube length, or wheelbase, or reach, etc.