60/40 vg/pg works fine in tanks, at least in my experience. I wouldn't go over 70/30 vg/pg though as the wick does get quite dry before it re-wicks (juice is too thick). Finding 24mg nic in high vg juice is not easy though, at least in mix's higher than those listed. I heard the new Subtank has a new rebuild piece that allows for higher vg content with ease. However, I cannot speak from experience on this as of yet