The Super Tank's are not the best thing Grievous has (debateable). Grievous has an incredibly vast number of heavy vehicles. Revan can't keep up with Grievous' production power.
If somehow Revan wins (which is completely illogical given what we know of both sides), G0-T0 wins. If Grievous beats Revan (completely possible), then G0-T0's chances are a little less but still possible. I think it comes down to Grievous and G0-T0.
The topic of Ventress' defection is interesting to consider. But wouldn't Ventress kill Revan for more power? Or would she not duel him to see if he is powerful enough to serve? She can beat Malak pretty easily, but can she beat Revan? She has faced Jedi Council members and proven victorious on several accounts.
Really, it doesn't matter if Revan wins or not. He will still lose to Exar Kun, who will win his battle.
I think Reven would do what Dooku did. Show her his power, through any means, and she will serve. Send her on a mission, and bang, she's yours. A mission that could inflict serious damage if successful. Say, destroying manufacturing plants, or stealing experimental weaponry. She would know everything about the CIS.
Also, even if Grievous beats Reven, he would have to come to Nar Shaddaa, which doesn't like being invaded. Would they be able to defeat the entire CIS? No, but they would do some damage. Add that up plus the mercs and assassins, bounty hunters and thugs, and you have a nasty gorilla fighting group to deal with, Grievous. And Grievous wouldn't be able to purchase the invisible ship finder thingy. But depending on G0-T0's pockets, a gravity well projector might be waiting for Grievous.