I'm not sure if Dooku's more then 80% of Sidious, but he's still a FAR better swordsman then mechanical Vader. Suit Vader lost all is finesse, and raw force power too. Although (I have no proof) but I'd think Vader would be powerful enough to block Dooku's force lightning with his hands (remember it doesn't actually touch you). And even if he couldn't, he could at least block the lightning with his saber as Obi-Wan did in ATOC, Vader is definitely more powerful force wise then AOTC Obi-Wan.
If it was a force battle I'd say its 50/50 between the two, it could go either way.
If it was a lightsaber duel, mechanical Vader gets killed 100% of the time. So since the force battle could go either way, but Dooku would always win the saber duel, I'm giving the fight to Dooku.