I'd get a 50 or 52. I think the 50 would be a better fit. Assuming you would go with a 100mm stem, running a slightly longer stem (110mm) would really let you dial in to the steering / handling. This is true from 90mm to 100mm as well. The 50cm has a 53cm TT while the 52cm has a 54cm TT.

I have a 32" inseam, you seem to have roughly 31.75", and I ride a 53.5cm TT on my fixed gear - on my road bike I ride a 54 - 54.5cm TT.

Remember, frame size refers to the length of the seat tube, which is pretty worthless IMO - the real measurement that matters is the length of the top-tube (TT).