Currently a reduce on (e.g.) long-array never ends up in the fast {{ArraySeq_Long.reduce}} function. Only if the user calls {{seq}} on it beforehand.
So:
;; Fast:
(reduce (fn [_ _]) 0 (seq (long-array [1])))
;; >2x slower:
(reduce (fn [_ _]) 0 (long-array [1]))