I found the charts to be right on for me as well - fit confirmed i had a really long torso and at 5’11" I am on 56 at limit of reach, but on a 58 I’d practically be sitting on the top tube.
For what it’s worth, a lot of people on slow twitch advocate going with a P2/P3 and just do an updated base bar that will give you way more for flexibility for same $.
I just got the tririg alpha one on sale and put it on my used 2016 P3, slammed it flush, all wires/cables hidden and an incredibly adjustable monopost front end that tests as fast as a P5 and looks amazing. Massive improvement over the stock 3T bar, and still uci compliant. It’s a brilliantly designed system and takes much of the fit and sizing risk away.