4,4vs6 is an interesting hand. Basic strategy is to split, the Hi-Lo index would be to hit at -2 or -3, I guess, but besides splitting and hitting, there is such a thing as deck compositions in which the optimal playing decision is to double this hand, amazingly enough. No need to go to details, since it's nothing you would pick right out using any standard count. It's also often so little in terms of EV for the hand between these decisions, along with the infrequency of the hand that qualify this for nothing more than the "fun facts" category of all things blackjack.