Currently we have following size hints in bundle:

data Size = Exact Int          -- ^ Exact size
          | Max   Int          -- ^ Upper bound on the size
          | Unknown            -- ^ Unknown size

however buffer allocation for vector has only two strategies: doubling for unknown and exact allocation for both Exact and Max. I think we should have three: unbounded doubling, doubling with bound for Max, and preallocation for Exact

P.S. It was also proposed to add lower bound to discussion