At 5’12”, I’ve tried 21”, 23”, and 25” frames. While one can certainly use seatpost and stem to achieve an effectively identical riding position across different frame sizes, my experience was that the 21” and 25” frames just “felt” weird vs the 23”. Goldilocks? I think maybe the c/g of the bike itself changes with the frame size, and maybe also the frame flex characteristics? I dunno. I have precious few years’ bike experience.