I have always loved using the Byz infantry and find that with the 100 you normally get great results. Gollum is right though, that if you don't have a better general (and battle skills), they may rout, extra men and all.

As to the CMAA, I don't know why, I often find these guys a liability. And yes, their speed is part of the problem, but I find they often rout too easily if the battle is a little tougher than expected whereas FMAA often hang in there and might even save the day. Go figure, the cheaper unit proves to be more valuable in this case for me.