I find the Derby scent very, very similar to Arko. Performance wise the two are also very similar but I feel the Arko lather is both thicker/richer and slicker than Derby but not by a huge amount. Derby is a somewhat harder soap than Arko to the touch.
Still on my years run with ARKO!!!!! (please note the correct spelling), I will need to restock before the year is up so any of you out there with excess ARKO!!!! let me know and I will try to come to some arrangement.