Well, if you are also interested in building up immortal characters, you can do the level up/down trick. Basically, when you gain a level, you gain + to almost all stats, even if its only .1 (and you wont see the change till 10 levels of +.1). And when you de-level due to a degenerator trap, you lose those same stats. But different jobs have different +s. You could train up a superfast powerhouse by de-leveling as like a bard, and leveling back as a ninja. Bard has the weakest +stats per level, and ninjas have some of the best, particularly speed. So you de-level a bunch as a bard, and re-level as a ninja. Each set of levels you will gain more speed/PA/hp etc

We're talking about characters with 999 hp 999mp and 40+ speed, but it required insane dedication

http://www.ffgurus.net/fft/?section=godguide

You can read up on the trick there