(Unboxed.Vector Char).takeWhile is much slower then Data.Text.takeWhile

Hi!
I know that Data.Text has different underlying representation, but no matter what it is, it should not be faster than Unboxed `Vector Char` when performing `takeWhile`. Both libraries implement `takeWhile` with the same signature of `takeWhile :: (Char -> Bool) -> X -> X`, so they are comparing `Char` by `Char`. Unboxed Vector know the shift between elements, so if `Vector.Unboxed.takeWhile` is 30% slower than `Data.Text.takeWhile`, I think we should consider it as a bug, right?