Same issue here:

CPU: AMD 8350
GPU: AMD 7950
6GB RAM
Windows 8 64bit

Most FPS drops when flying in the heli showcase (18-20fps@the start base while looking in the startup direction) and in coop Multiplayer, cant be improved with change graphic settings lower. Only reduceing visibility / objects helps.
In infantry showcase or editor the fps are aroung 30-60(-120 while scoping).

Iam an old OPF Player and love the game already, i really hope BI will be able to fix/improve this!

thats right with the AI Problem,
in the underwater showcase dropped my FPS immediatly after i disarmed a mine, it triggered the AI to come with the boat.

But otherwise its a big different for the FPS where you are and where you looking at, in the ocean i have about 45-60fps when i look down to the ground an under 30 when i look in the direction of the open sea.