Bingo.
I was in the same place between 54 and 56, and mail ordering a bike.
I bought both, tried them out with various stems, and kept the one I liked better.
Seriously, if you are spending the coin on a new bike, its worth $50 shipping charge to try them both out
(FYI, I bought a Canyon, and the return shipping was $0. There was zero cost to me trying out two bikes).
Yes, stand over height can be critical (especially if you have a horizontal top tube).
I ended up with the smaller one because I liked the more lively handling, the shorter reach ultimately was more comfortable, and I liked the standover height.
remember, with more seat tube exposed, you are going to get a lot more comfortable ride with a good carbon seat post.
(I put a comfy high $$$ carbon seat post on a bike that fit me like a glove, but had very little seat post exposed. There was zero comfort benefit from the carbon seat post on that bike).
All things being equal, the shorter frame will be more lively, the larger one will be more stable.
good luck with your choice