I think if we had seen the PS3 version release on the current engine, a game like Final Fantasy 13-2 would be a decent benchmark as to how the game would run. The engine is also undergoing surgery, so it will most likely perform even better than what I'm about to suggest.
No spoilers from me, har har! And mild spoilers are in the hidden boxes (which may not seem like spoilers to some, but I've been clocked on this several times).
Three tests:
1) Get into a battle with rainy weather, engaged with five or so enemies. Have your second ally as the Ravager role and use a large ally as your third character. As the player, cast Ruinga.
Academia 400, beyond the collapsed bridge where you fight flying and hulking Taxim ci'eths, usually 5~6 enemies at a time. Have a behemoth as your monster ally.
2) Go into a location with a dense population. The characters may have less detail than the player characters. Rotate the camera a few times.
Academia 4XX in the northeast section of the map.
3) Get into a battle with multiple gargantuan enemies. Cast Ruinga.
If you are content with the frame rate and the graphics of:
your the main character (may be a cross between main and lower detailed NPC),
monster detail,
attack effects,
the environment
You'll be golden (rough estimate)