Hi, Currently, I ride a 50cm FG. I'm planning to build one up soon; and i want a perfect size. So, I'm 5'2 - 5'3 ( short rider. don't judge. ) w/ about a 28 inseam. I'm aiming for a perfect size with good clearance. Thanks.

Well, it has a lot to do with personal choice. Is your bike right now too big or too small? I assume it must be one or the other if it's not perfect.

Also, standover clearance is not a good indicator of fit. It's probably the least important of all the measurements.

We cannot tell you the perfect size over the internet. That's like getting fit for a custom suit over the internet.

The "perfect" size will come from a proper bike fit. A ballpark size will come from some online calculator or something.

Also, there is no such thing as a "fixed gear size". It's no different than getting fit for a road bike. Search for road bike size charts or something.