Dragonball Kai man, that's where it's at these days. They went back and digitally remastered all the old episodes and cut out all the crap of them standing around doing nothing. Just to give you an example of how much they've cut out; previously Goku goes SSJ in episode 95, in DBK he goes SSJ in episode 47! They've cut out almost 50% of bullcrap! Definitely go and rewatch it.
Regarding Battousai vs. Yama: firstly, Kenshin wouldn't be able to sense Yama. Now if we open this up in the battle pits and disregard that, we have only seen the slightest fraction of Yama's power, and no precise indications of his speed except that he's fuckloads faster than Shunsui, who so far along with Yoruichi appears to be one of the fastest shinigami. Kenshin would be doing well to actually be able to even breath under Yama's unreleased reiatsu let alone his bankai. And which Battousai? The serious one ie Samurai X OVAs or the idiot fool one from Rurouni Kenshin the anime?