I'd wait until April 2014 to stock the LMB and CC together. At that time I'd stock the next size larger CC, probably 6"-9". Price difference would be minimal, and if you fed them a good food, you could be harvesting them for the table in the Fall.
Just remember that as a general rule, I've found when given a fish size "slot", a greater % of fish delivered are usually on the small end of the slot vs the large end.