Given the geometry I think AO is a bit of a time-waste, its not going to add much more than what good shadows would. And while using GI means you don’t have to be clever with lights to get the same effect (and you could easily given the simple geometry of the scene), you will certainly slow your render times down with it.
But in fact it might be all the 1 dimensional edges having to be considered by the AO and the GI (and the textures) that are giving you grief. As more of those edges turn to camera it may become harder for the AO and GI to calculate. Both of these features weren’t really meant to consider 2 dimensional plane edges in their calculations.
Also – how many cores have you got in that i7? That looks like the recommended chip for AE where it wants one big superfast core. Cinema prefers many cores.
How big are your textures? They only need to be as big as they will ever get in the render. So if a face only ever gets 100 pixels high in the render then the texture only needs to be 100 pixels high as a texture – anything more is a waste of ram (double that if you are using best antialiasing). I’m wondering if the textures are too big and because they are animated, your ram is getting chocked full. So it has to flush and reload every frame. And jpgs are fine for this kind of thing. Tiffs or PNGs will add to the memory load.
Finally, if whats in the frame changes considerably during the camera move, more stuff means more time and going from 36 seconds to 45 seconds isn’t out of the norm. You may find once it gets to say 100 frames the time plateaus and it doesn’t get any worse.