I'm thinking about buying an old rigid MTB to fit with slicks and fenders for commuting. It was always my understanding that you go with way more standover on a MTB than a roadie to give your crotch more space when bouncing around offroad. This bike will never see dirt.

I ride a 16" MTB and a 49cm road bike. Do I go with a 16" for the commuter or would I want to go bigger?