99999 is doable, I had yuna and lulu doing it with attacks and I hadn't completed the sphere grid (as in optimising it).Here's the video. They're much weaker than I had them in the end, but at least all my hard work getting Yojimbo to be my bitch is still there.
I have one of Yuna's sphere grid but it's far emptier than when I left it on my other save so didn't bother to upload it.
Hits max out at 99999 so I was talking utter shit here. Must have been 20-30k. I definitely have memories of Yuna one-hit killing bosses, but mustn't have been Jecht like I said earlier.