for S4's to work well with boost, do you need cam sprockets to fix the overlap, or will they be fine without them?

You don't have to add the adjustable sprockets, but you'd be missing out on a couple of horsepower and failing to eliminate a couple of weaknesses that could hurt performance. I seem to remember something about how overlap and combustion temperatures being related; reducing overlap also reduces temps, which at these levels is a good thing...somebody jump in and correct me, here...