Don't forget, Mace himself states that Kenobi's saber skills are above his own, nobody ever breached ROTS Kenobi's blade with their blade (Anakin breached it with his foot to kick Kenobi), and that was ROTS Grievous that Kenobi beat, and it wasn't that easy. Yes, I doubt Yoda would pwn Grievous with sabers though he definitely would take it. Force duel Yoda obviously and all out I say Yoda wins without a lot of trouble but I doubt he would pwn.
I say yoda for sure if he can use the force (scenario 2 and 3) But if restricted to only using it to propel himself (think of the double jump over Dooku) he might have some trouble. Grievous knows the tricks of ataru, and mace did say that Obi wan had the best chance of victory. (yes I know its an in- universe source)
1. Close, but yoda
2. pwns
3. Yoda w/ less difficulty than in 1, but some.
First of all, GG was weak from having his ribs Force Crushed by Windu, hence the cough in the movie. Secondly, Obi-Wan's style was the perfect style to fight GG with, as stated by Windu.