Old Ben would have still been a Soresu master, and we saw that age didn't take away Dooku's abilities.
I give Kenobi the close victory against Kao if it's an unemotional fight...though Kao might win if he's as determined as he was while fighting Vindicus and Malgus.
S_W_LeGenD
Darach
Stigma
Kenobi becomes more powerful than Darach can possibly imagine.