I'm actually stuck on Sin Overdrive myself - I've got all the celestial weapons, aeons, and I'm maxed out on the sphere grid minus the Lvl 4 abilities and going over to friends' sphere grids..

I know you can farm Lvl 3 & 4 spheres in the Omega Ruins, but.. I don't wanna! lol...

XII is easy. Grind out on the levelling.. I actually equipped the um.. Golden Amulets to double the LPs earned and then when I got enough to fill up all of the stats/abilities and most of the weapons, I switched to the Embroidered Tippets just before the Pharos.

I beat the game with my main team at level 55/56 (my back ups were only at 37, but I never had to use them - even for Quickenings). Sorry. That was off-topic.