And Thad, both are incorrect. It should be kBps and mbps. , though I am not sure whether the 'k' can be capitalised or not.
Cheers
Usually, the only character that is compulsorily case-sensitive is the b(it) & B(yte). Otherwise, I've found that industry usage includes upper- and lower-case k's, m's and t's.
Here's the definition of units of measurement for network traffic. Probably more than anyone wants to know...