When I was sorting out my x68 sizing, I took an existing well fitting bike and measured reach, stack, and drop (by measuring bar height from floor and saddle height from floor ). I was then able to approximate whether I could get the drop to work with acceptable spacer stack, and what stem was needed.
I was between sizes as well, using my measurments I was leaning to a 42 with max spacers and a 110, using Specialized's chart I'd end up on a 52 with much less seatpost and a shorter stem. Experience then took over-generally, I prefer bikes that I feel like I'm "in" rather than "on" and immediately gravitated to the smaller size frame, 110 stem, and live with full spacer stack. I love the bike and the fit, and I'm 65 with an injury history so if it works for me, yada.