Level 9 to 16 - Requirements and Benefits
As I've just recursed again, and couldn't remember an XM pool value, I dug up the old levels image. This is the 'gold standard' one that many people have used for years, but only if you know to look back at an old reddit post from 2015 (or have it bookmarked).
Figured I'd put it here for an easier reference.
All credit to @rediguana and @joniak (assuming they still play and/or have accounts)