I JUST got through this dilemma, and I'm actually STILL undecided after purchasing the black m/l lambskin in SH this past weekend. I tried on both m/l and jumbo at the store, and honestly they both worked perfectly. For reference, I am 5'5 and 115 pounds.
It all came down to how I wanted to use the bag. I already have several black chanels for daytime, so I chose m/l. Its on its way (being shipped to me) and I am very tempted to swap it out for the jumbo with ghw because I think I will use the jumbo more. So its definitely an ongoing issue with a lot of ladies!!!
I think you should definitely try both on, maybe even take a few pictures holding the bags to get a different perspective of how each size looks on your frame.
It all came down to how I wanted to use the bag. I already have several black chanels for daytime, so I chose m/l. Its on its way (being shipped to me) and I am very tempted to swap it out for the jumbo with ghw because I think I will use the jumbo more. So its definitely an ongoing issue with a lot of ladies!!!

I think you should definitely try both on, maybe even take a few pictures holding the bags to get a different perspective of how each size looks on your frame.