Well, I don't know where to peg Kaioshin at. He got way stronger after fusing, but if Vegeta were still the one who got to stay in the planet to battle Kid Boo while he didn't even suggest aiding them, I think Vegeta's still considerably above Kibitoshin. Vegeta is considerably above SPC too, so this could be an interesting battle. I think they may be in the same realm of power. I'd say Super Perfect Cell has got, perhaps, a power advantage, but if Kibitoshin plays smart I think he can stop him steady and maybe apply some good strategy to pin him down. Idk tho, could go either way. The scaling of Kibitoshin isn't made except being decently below SSJ2 Vegeta, who's somewhat above SSJ2 kid Gohan and in turn considerably above SPC, imo.