4,4 vs 5 or 6

In a 6 deck double after split game I've always split 44 vs 5 or 6 except with negative counts above 1 which I try not to play anyway. I recently read (here I think) that at high plus counts it is better to double, which makes sence as you would most likely end up with (2) hands of 14. At what plus count is it more advantagous to double rather than split