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I want to get the differences between these models straight. What are the precise differences between them? I have heard the rim is a bit different, but how? And how is the cup depth and shape different/similar? I read the bore on the 48 is 8.5 and the 50 is 8.3--minuscule difference there.

The difference in bore makes up for a difference in throath passage area of very close to 5%.

Minuscule or not, that depends. If you miss phrase endings with the larger bore, then you will find the difference noticeable.