House edge for double deck w/double on 8

I know what the house edge is on the usual double deck pitch game where doubling is allowed on 9,10 and 11. I play at an Indian casino which also allows doubling on 8 including soft 18s. The other rules are DAS, H17, split up to 4 hands, no resplit Aces, no surrender, peek. The house edge without doubling on 8 is 0.51%. How much lower is it with doubling on 8s. Thanks.