You don't have to train that much, you're ready as your party is now. Just do the AP trick a few times till you're maxed out and you'll be out kicking some Dark Aeons around in no time.
AP Trick:
Requirements
-Overdrive to AP ability
-Monsters captured in Cave of the stolen Fayth
-Comrade overdrive method
Optional
-2x or 3x AP ability
-Double/Triple Overdrive Ability
-Auto-Phoenix ability
I'd recommend
Overdrive - AP
Triple/Double AP
Triple/Double Overdrive
Auto-Phoenix
(The easiest way to get the 3x AP Ability is as follows: capture 4 of each
flying eye monsters. Omega Ruins, Mi'ihen, Thunder Plains, Gagazet, and
Macalania are the 5 regions you should target. You'll unlock One-Eye at the
monster arena, and fighting him over and over again should yield weapons
already with Triple AP.)
How to do it:
Just fight Don Tonberry over and over again while equipping the character that's gonna level up with the above described weapon and set his/her overdrive gauge to comrade, this way with each hit you receive from Don Tonberry's karma will give the character in question loadz of AP (99 sphere levels max). If some of your characters have killed a lot of fiends the damage Don Tonberry does to them will increase drastically and so will the AP gained by the character with the overdrive to AP weapon/comrade overdrive gauge.
This is by far the best/fastest way to level up so i wouldn't go running around in the Omega Ruins for hours coz you don't have to (unless you need loadz of gil ofcourse <img src="/images/graemlins/tongue.gif" alt="" /> ).