For Demo - the stats surprisingly enough scale without plateauing pretty equally. This means that as long as you maintain a balance between haste, crit, and mastery it makes little difference which you choose as your highest. Below is a link to the plots I simmed last night. I wanted to see where haste or mastery would become better than crit, if ever. Just remember, even with 4k+ haste, SF and SB are both going to still have a 1.7+ cast time.