road bike fit 48 vs 50 input?

[bcipam]

Mmmmmmmm 50 sounds tall for someone your size. I'm surprised the 48 fits! It seems like you would be better suited on a 46 or 44. Are your legs and arms really long compared to torso length?
I'm 5'8" and ride a 53 Lemond. The Lemond has a long top tube so most likely I would be a 54 or 55 on some other bike but keep in mind I am 8" taller than you.

It is not unusual for the bike sizes to differs as geometry changes from one style to another. What you should be looking at is 1) reach - ie the top tube length. Can you comfortably access the shifters and brakes without bending forward too agressively (think like a racer during the Tour de France, back almost flat and level, arms bent) and 2) then is the standover adequate. The top tube length is the most important. If one of the bikes is woman specific and the other not may explain the difference in measurements but bottom line is how do you feel on the bike? Are they actually sitting you on the bike or a fit bike? Have you pedalled while seated on the bike? Does it seem comfortable to you? Or is the position agressive (ie you are bent over and stretched out to reach the shifters)? If agressive is this what you want? Do you feel you have to tippy toe to pedal or can you pedal with your foot flat?

Sometimes a bike shop needs to move a bike - many people buy the wrong size. If it's a question of not fitting on either size, get the smaller not the larger bike. You can always make adjustments to a smaller bike but to a larger, you are just stuck.