At the moment I am running a 100mm stem with no spacers and feel a little stretched out on the hoods. The drop is not super aggressive due to the longer headtube of the 56.
So will moving to a 54 make the reach a little less and also make the position more aggressive (which I want)?
I should also mention that I am 5’10.5" with arms that may be on the short side. I ride with a mid-foot-ish cleat pos (cleats pushed all the way back).
Have you tried a smaller stem? I’m the same height as you and I have a Trek Madone in a 56 and a Felt B2 in a 56. I tried a 54 Felt and couldnt get comfortable. I kept bumping my knees into my elbows. I aparently have long femurs and shorter shins. I run the stock stem on the madone and a 90mm 6 degree Ritchey flipped to flatten it on the Felt.
I’m 5-10 and ride a 54cm Soloist Carbon with a 110mm stem. I definitely wanted the 2 cm headtube (shorter) on the 54 vs. the 56 for aero/positioning reasons. Fits me great!
Matching current position would require 120 stem and 15mm of spacers (assuming you have -6deg stem such as FSA). Clearly you could reduce the reach by using 110. If you wished to increase the drop you could, over time, reduce that spacer height too.