Stack is the place to start. When I buy a frame, I want a stack of about 540mm WITH the headset top cover and spacers, if I can use a -17 stem. If I'm using integrated bars with a -6 degree angle, I only need a total stack of about 525mm. Reach can only be compared at one stack height. If two sizes are being considered, subtract 3mm from the reach of the smaller frame for each 10mm of stack height difference, This assumes that spacers will be used on the smaller frame, to produce the same total stack. The stack values on geometry charts don't include the headset top cover or any spacers.
I also have a range of reach of 370-380 that I look for, to keep the stem length in the 100-110 range.
With a 725mm saddle height, I get a saddle to bar drop of about 115mm.