Before the Jecht/Yu Yevon bosses, I was pretty strong, most characters has 9999HP, and really high Strength due to a lot of grinding I did inside Sin before I entered the final battles, but I did have problems with Jecht, but nothing a little thinking couldn't solve, now i'm on my way to having max stats (255 on everything, and LOT's of HP).

By the way, this is my third playthrough i'm talking about, and hopefully my"100%" file eventually.