Count Dooku and Darth Vader vs Darth Sidious
Both apprentices believed that by having an apprentice they would be able to defeat Darth Sidious. These two combined are more powerful than any duo that the two with their apprentices could ever make IMO. So with that coul they take down Sidious. This will be Vader in his prime and Dooku in his prime. ROTJ vader and ROTS Dooku and ROTJ Sidious.
Can these two defeat Sidious.
Round 1. Sabers
Round 2. Force
Round 3 all out.
Battle 2. If Vader and Dooku lose than they get Starkiller.