Of course, that's only assuming Count Dooku takes on Kar Vastor. If, like in kamikz's account, he were to take on Asajj and Obi-Wan instead, then Count Dooku can tool Asajj Ventress with comical ease if he were to utilize the Force, as was displayed in Dark Rendezvous:
"Her face went pale. Dooku lifted that one finger, and this time he tapped it in the air, as if pushing a needle into a pincushion. Ventress crumpled to her knees. Her voice came out clotted with pain. Dooku made another little patting motion, and Ventress slammed to the tile floor."
This would indicate extreme dominance, and superiority over Asajj Ventress in terms of the Force. Count Dooku is also the better duelist, so I'd say were Obi-Wan and Asajj to take on Count Dooku, she'd be tooled. Likewise, Obi-Wan would also lose to the power of Dooku, whether it's a prolonged duel, or with the Force. Most likely the latter given that his experience with facing Obi-Wan would dictate that it's Obi-Wan weakness.
As for Vastor and Skywalker, I'd agree with kamikz that it'd be a hard fought duel, but Anakin would more than likely emerge the victor if it's not on Haruun Kul. Even if the duel is still going on, Count Dooku would thus be free, and aid Anakin. Together, the RotS duo would more than likely win in that scenario.
Originally posted by Prodigal Knight
From the way I see it, I see Dooku getting killed and then the duo wtf pwning Kenobi.
Why would the "duo" [Asajj and Vastor] attack Obi-Wan? He is on their team, you know. 😛
And if perhaps, Kar engaged Dooku instead, and Asajj helped - I'm not sure. Anakin should be able to defeat Obi-Wan by quite a considerable amount of time less than their duel in RotS was, depending on the setting. The more important thing is the mindset of Anakin.
When the OP said that Anakin and Dooku were as we saw them in the beginning of RotS, I'd assume he meant the phrenic state, as well, which was described as being "clear as a crystal bell". In that case, then he would definitely defeat Obi-Wan, albeit through a decent duel.
I don't even know much about Kar Vastor to make an accurate assumption towards this scenario (mainly the time), but I can only gauge that he's not as powerful as Count Dooku while not on Haruun Kul. Nonetheless, from what is said, he'd apparently give him a good duel. If Asajj could add in strength to Vastor, and defeat Count Dooku than Anakin will probably go down to the remaining duo (assuming Obi-Wan's dead at this point).
However, if Obi-Wan is dead, and Dooku is still fighting Vastor and Asajj - I can see Team Skywalker taking it, as Anakin would come to the rescue.