I just finished defeating the four Elemental Fiends in the Giant. For most of this battle, I had both Haste and Berserk active on Cecil and Edge. When I do this in FF2US, the battle is completely ridiculous -- Cecil and Edge take actions every time you blink, and I can hardly even get a Fire3, Ice-3, or Lit-3 in edgewise. In FF4A though, it almost seems like Berserk slows them down. Before I had Berserk on them, they seemed to be taking actions faster. Once I added the Berserk effect, it seemed that their ATB would fill up, and then they'd wait for almost a full round before attacking.
This is only my second time through FF4A, and the ATB peculiarities are really starting to get on my nerves. Characters will spontaneously get to take two actions in a row, and their ATB gauge gets all screwed up after their second action. Or Rydia's ATB will fill up while you're choosing an action for Edge, and then Cecil's ATB will fill up, and your next action goes to Cecil despite Rydia filling up first. This can go for entire rounds, with Rydia not getting to take an action until Edge has gone
again. I believe the game just goes through your characters in their party order to see who's full, instead of keeping track of who filled up first. I don't recall 2US having this behavior, but it doesn't show you an ATB gauge either.
If I ever extend my FF engine project to attempt to play FF4, I don't think I'll end up providing a "true to the original" option. Too many versions of this game with too many different bugs.
We have EVEN MORE themes now, but some old ones are gone...