If the merit is equal, so is the reward - it is the same DEGREE. This does NOT mean the reward is of the SAME TYPE/KIND. For example, St. Paul's reward, being a priest, a virgin, preacher of the Gospel, etc., would be of a different KIND than that of, say, St Henry the Emperor or St. Louis IX, King of France.
There are many mansions in our Father's house.
Our Lady is the Queen, and her merits so far outstrip those of everyone else that it cannot be grasped. The merit of a deed is based upon the intensity of the charity involved, not the state of life to which the person has been called.