in a lightsaber duel Kenobi would be able to hold Bane off for a lengthy period of time. Bane would probably win but he would have to work hard for it.
In the force, Kenobi is very powerful but his defenses are lack luster and have been broken multiple times by lesser force wielders than Bane.
I love Kenobi but the only chance he actually has is if Darth Bane forgets that he has the Force.