Faunus, I'm not taking much a stance here once way or the other, but I'm certain Bane is bigger than Kun and extremely strong....In the physical department, I would wager he does have at least a partial strength advantage over Kun-indeed, over most humans.
Although it's true Bane was incapable of defeating Kas'im with sheer strength, Kas'im, I believe, was described as extremely muscular with every muscle perfectly tuned, along with his skill-though, granted, this applies to Kun as well, likely.
As for Kun's weapon: It's extremely difficult to get a fair grasp of the proficiency and effectiveness of the technique since Kun uses it against two people who lack any feats of their own-Vodo and Ood. I'm not disparaging Kun's skill with it-he's certainly highly proficient as a duelist with the double bladed saber and Bane can't know all of his moves-by the same token, Bane's from an era of saber combat more advanced and trained by one of the best, so it's safe to say he could adapt in the duel.
Another problem for kun are those orbalisks, but given he can slice through Mandalorian iron, with enough power, he could probably cleave through them-whether he could do so in time is a bit up in the air.
Another factor ends up being speed and given the lack of proof for speed in Kun's department-anyone correct me if I'm mistaken- but I think the edge goes to Bane there...
All in all, this is pretty up in the air.