As long as you keep the 3D slider off, it's 30 in battles, or my eyes really can't see any lag.
When you idle in battle some of the scenes have a very noticeable drop. Doubles, triples/rotation and Swarm battles are also pretty heavy on the dropped frames. Some of the more intensive moves have a bit of slowdown as well, but those are over fairly quick.
If it happens anywhere else, it's too minor for me to notice.