Best Use of permanent upgrade slot ? :: Cookie Clicker General

permen4d slotPermanent Upgrade Slot 4 (400,000,000) - Unlocks a slot to place an upgrade in. This upgrade will last through all ascensions as long as it's in a slot (--) Heavenly UpgradesThe list of what to use for each permanent upgrade slot is located after the impatient guide, or use the sidebar to navate to it. Please note