Hey, I have a 47 X 56.5 custom bike with a sloping top tube among others in varying std sizes. A std frame a 53 or 54 fits my "stand over" (sorta) but the top tube is too short as I have a long trunk, so I normally buy a 56 and let my "boys" tickle as the top tube length is more important. A short top tube makes your rear wheel jump off the ground when climbing or sprinting hard. I'm careful with the getting on/off part. Most bikes are "square" with equal top and main tube lengths, some, like some of the Italian brands, are "short" with the top tube 1cm shorter than the seat tube. A few companies make em long (+ 1 cm on top) and a few offer square, long or even short options in their production models