So I just pulled my first 4* mana troop.(barbaic assasin) And I’ve seen that you want them to be at least a level 11 to get a good bonus from them but my question is at lvl 11 does it make a normal mana gain hero into a fast or does the troop have to be maxed for that kind of buff?
The only speed that goes to a higher tier is Very Slow -> Slow, just due to the way that mana bonus percentages calculate.
Check that thread out, for key percentages
At level 11 a very fast hero will need only 6 tiles to charge instead of 7. If you have Jackal or gravemaker or Kage or Victor - they will benefit greatly.