A blow off valve is needed vent excess boost pressure to the atmosphere when changing gears, etc. What I am wondering is for the adjustable BOV's what psi would I adjust it to if I were running 15lbs of boost? Would I adjust it to 14, 15, 16 lbs?
They aren't really adjustable for the amount of boost you run. The more boost you run, the harder the valve closes itself.
If anything, you'd just make sure that the spring isn't so tight that it won't open when you lift...like if you lift and it still has some surge/flutter, you'd want to run less preload.