Originally Posted by Darth Hord
You have to remember though he could never truly become as powerful as he could have been after Mustafar. I'm fairly certain that in vanity fair magazine GL said Vader was 80% as powerful as the emperor (OT, version I think).
The latter I agree with, the form while is G-canon, never made too much sense to be, due to the fact Yoda said; "Size matters not". In otherwords, surely Yoda shouldn't be as powerful as other force users as he's much smaller - it's the same logic as Vader's Force Ability being reduced after Mustafar.