Not sure about the maximum allowable with AIC - but catalyst currently has a maximum playback resolution of 4480 x 2600 - which can accommodate RED content.

So your movie could be 3840x1080
...but it doesn't necessarily need to be - it could be smaller, at the same ratio.

7-8 layers of 1920x1080 @ 30fps (assuming a sensible data rate of about 60Mbit/s) is about the maximum currently possible with a 2011-2012 MacPro, SSD and a Quadro 4000.
It depends upon the data rate of the movie and the bandwith available from the SSD over SATA.

You will probably be able to playback more movies at lower resolution, and thus lower data rate. You need to test this yourself on your system -as results can vary.

If your frame rate is set to 30fps, (and playspeed is set to 100%) then the frame indicator should normally say 30fps.

However, if it is showing a lower frame rate - then it is dropping frames.
With what you have described - if you are playing more than 8x 1920x1080@30fps movies - then i wouldn't be suprised if the frame counter is showing less than 30fps and the movie not playing as expected.

One question: Why are you trying to playback 16 HD movies at the same time?

S