I was in that weird 48/50 gap as well. Went with the 48, which makes it impossible for me to wear anything thicker than a very thin knit underneath it (definitely no tailoring) but oh well. Arm holes are crazy high for an overcoat. If I hadn't gotten it at a good price/needed the coat to be my only car/overcoat, I probably would've passed.
Consistent sizing is a pipe dream I suppose (I own everything from 48 to 52 and M to XL).