Jax, if you haven't gotten a dry suit yet, you might find that Rob (or at least Jen) has a different attitude towards the Fusion now. Lynne and I were both diving our Fusions this week. They are a very nice suit for caves, OW, warm or cold. IF you are going to use them in cold water, just make sure you get one big enough to easily get the heavy undergarments in.
It sounds like you and Lynne are about the same size and she is very comfortable in the Sm/Med Fusion -- but she also wears my L/XL as her backup suit. She couldn't wear the White's boots but I find them wonderful
I have my Fusion! It's the 2XS-XS; The only time it is tight is when I bend over straight-legged to kiss my knee . . . I don't think I'll need to do that much when I'm diving. That's with the Xerotherms, but I'm not seeing much difference in the Arctics.