I guess the question is how would you be using a BB on a mark 3?...both my mark three's have so much gain on tap there's no use for a pedal save for maybe the clean channel is that what you mean?otherwise if your mark 3 doesn't have enough gain, you should have it checked out.
+1
If you play your MkIII like many here...ch3 for metal/hard rock...then you won't like much/any boost. There's so much on hand ant further loading the input will only bring noise and fizz.
But, if you are like me and no longer use ch2 and 3, then boost pedals work spectacularly well. The EP-Booster is my pref right now. Again, this depends on the music you play and desired tone/drive.