Quote Originally Posted by Skyblade
Um, I haven't had the game this long, but I'm fairly sure that having multiple pieces of equipment with the same ability doesn't change the boost given by that ability, it just changes the rate at which you learn that ability. I'm fairly sure that even if every piece of equipment had HP+20% on it, you'd still only get a total HP boost of 20%...
That's what I was thinking. The only combination I've got that works so far is the HP+10 and HP+20 to get HP+30, which still isn't that much.

I must say that's a shame that HP+20 is the highest you can get, I always like getting up to maximum HP on Final Fantasy games.