Found this topic (have you tried the search option?):
http://forum.mikrotik.com/t/wireless-fp-ce-ceee-ec-ecee-eece-and-eeec/78748/1
By selecting Ceee (or any orther 4 digit option) you will get 80MHz channel width.
Make sure you select the channel manually ( I totaly dislike the auto option) and turn down tranmission power (search for antenna gain 
)