Question about splitting 4s and doubling 8

DD >= #
8v3: +17
8v4: +12
8v5: +7
8v6: +5

Split >= #
44v3: 14
44v4: 7
44v5: 3
44v6: 0

What happens if I have 44v6 at a true count of +6? Should I treat it as an 8 and double since it exceeds the index for 8v6 of +5, or should I split since the index says anything greater than or equal to 0?

For a single deck game where DAS and resplitting aren't allowed, is it better to double or split?

If DAS and RS4 are allowed, like in most DD games, my gut tells me to split instead of double since there is the possibility of resplitting and doubling after splitting.