I tend to go for the larger one, just 'cause larger frames have smaller seat angles... I do better with a 73 degree seat angle. I hate 74 seat angles or above. 73.5's I can manage.

But if I'm on a 74 degree seat, I'm always shoving my butt off the end of the seat to get to a position that my knees & legs are happy with for pedaling... and I don't feel like I'm riding as fast as comfortably.

But then I'm happy with about a 540 mm reach and don't use shallow reach bars either.

If you want to be aero, get the smaller size, if you want to be more upright, get the bigger size.

Maybe see if the bike shop will set up the larger frame for you with a shorter reach & more shallow bars to try on a trainer. Just sticking putting a new stem and handlebars on it while the other handlebar hangs to the side with shifters might work for sizing.