Wulf Ratbane
Adventurer
I tried this. Doesn't account for effective caster level (as paladin and ranger cast at 1/2 HD) and if taken into effect with the sorcerer you still end up with the same inherent difference as my results above with the sorcerer being 50% higher than the wizards and the druid and cleric being more powerful than the wizard.
50% higher in total, or 50% higher for just that portion of CR (spellcasting)? I assume the latter.
First find a base methodology that looks right (and mine does, based on UK's other methods). Then massage that base factor until that gap between the casters rings true to you. .005 too high? Try .0025.
And then-- again, my larger point-- if you're close enough across 20 levels, you're close enough.