Answers to questions like that can be found using my house-edge calculator by changing a rule and noting the effect on the house edge. Normally I would make you do it, but I’m in a patient mood today, so here you go:
6 decks, dealer stands on soft 17: 0.0726%
8 decks, dealer stands on soft 17: 0.0758%
6 decks, dealer hits on soft 17: 0.0882%
8 decks, dealer hits on soft 17: 0.0916%