I did some analysis. These are all the Steam Pillars of Eternity 'SKUs' (Steam calls it 'subs'):
https://steamdb.info/app/291650/subs/
Some of these are "developer only", some might be only for internal testing.
The SKUs you can buy at Steam are:
Hero (China, CIS)
Champion (China, CIS)
Royal (China,CIS)
The pre-order SKUs are:
Hero (CIS)
Champion (CIS)
Royal (CIS)
The upgrade SKUs are:
Champion
Royal
The backer only DLCs are:
Backer Item and Achievement
Backer Pet, Backer Item and Achievement
The SKUs containing these backer DLCs are:
Backer Hero Edition - Pillars of Eternity + Backer Item and Achievement + Making of Documentary + Pre-order Item and Pet + Cookbook: 62849, 63750
Backer Champion Edition - Pillars of Eternity + Original Soundtrack + Campaign Almanac + High Resolution Game Map + Making of Documentary + Ringtones + Wallpapers + Backer Pet, Backer Item and Achievement + Pre-order Item and Pet + Novella + High Resolution Concept Art + Cookbook + Collector's Book: 62850, 63751
Backer Royal Edition - all Backer Chamion Edition content + Strategy Guide: 62851, 63752
The funny thing is, none of the Backer Editions contain the Champion and Royal Edition DLCs (whatever they are):
Champion Edition Content
Royal Edition Content
These were removed from the Backer Editions: 62850, 63751, 62851, 63752!
The purchasable (or pre-orderable) Champion and Royal editions don't contain the backer only Cookbook: Cookbook.
I hope I have confused you Royally
PS. My conclusions: the only difference between the Champion and Royal Backer editions is the strategy guide. Steam should add it without loosing the backer bonuses, if you purchase the Royal Edition Upgrade.