We are never going to know how strong Yoda actually was. He was probably THE posterchild for the light side of the force. I guarantee you there were things he knew and could do, that would blow everyone's mind, however he refused to do it, due to the fact that he was soooooo light side. Even in the movies, Duku and Palpatine himself, were only a match for yoda, they never beat him. The duel with Palpatine, imho yoda just gave up. If yoda completely cuts loose and goes 100 percent (which I don't think we have ever seen, i think at the most we have seen 60 percent of what yoda could really do) yoda would wipe the floor with any other force user out there.
That's a decent argument, but there's some speculation involved here.
Why would Yoda only go 60% of his power against Sidious? That just doesn't make since. Yoda would have given it all in that fight.