Originally Posted by Moisture

You obviously need to know stem length. Top tube length will also play a factor. Also important to consider saddle setback, hence which is why it is important to be able to try the bikes in person and make adjustments to saddle height, tilt, angle, setback, handlebar angle/position etc. as needed before comparing.

generally speaking, you can compensate for less or more frame reach by changing stem length accordingly, that is assuming that frame stack is roughly the same.

You can always manipulate the "effective" frame stack/reach with different stem lengths.

Don't forgot handlebar rise , reach, drop degrees whatever depending on flat/drop bar.

Originally Posted by Moisture

once frame stack starts to change dramatically, this is when comparos become slightly more difficult. some bikes have a long headset cup which changes the lower stack you can use. Others have cut steerer tubes. others dont. this is why stem length/degree combos are useful to achieve the effective handlebar stack/reach position you want.

Your stack/reach comparo is a good start. but dont be too critical, because like i mentioned there are other factors which may change your preferred fit. different frame geometries can work similarly well for you when comparing from bike to bike.