[RWebb]

they are all made for one or the other thickness walls - so, yes if already ordered; no if not

one trick I've seen is to use 2x4's and offset them for noise isolation and extra insulation

you can always get better insulation with a single row of 2x6 than with a single row of 2x4, assuming the same materials are used in each - people get high insulation with 2x4s by using higher R value insulation, but you can use that with 2x6s too

you will want to seal the eff out of the house - there are special sealing materials used here for the most thermally efficient houses - a neighbor can heat his new house with the body warmth of 4 people for most of the year

highly sealed houses need special moisture control