Originally Posted by Camilo

The wheel sizes you mention are different. One is a 700C the other 650B. And there's no such thing as a "650bX40c. Widths are measured in MM, not "C". The letter in a wheel size does not refer to a size, but a naming convention, such as 700 tire would be 700c X 38 or 700X38c and the 650 tire would be 650bX40 or 650X40b.

Take a look at the Continental Terra Speed Good reviews for rolling resistance on pavement as well as mild traction situations. Probably not good for actual mud.