Thanks for the updates.
When I first saw #52, it looked like the "b" was floating compared to the rest...then I read your comment. I understand what you were going for but I'm not sure about it as is. How about exploring a version with a smaller "b" (exponents are usually smaller font) and a version with the "b" in the normal position.
I really like #42 and have gotten very positive response from associates. I like the darker blue compared to the other (more serious looking), but I'm wondering if you could do a version that was just a little lighter?