Hey Doug.
My advice with the ToUCam/SPC900NC would have been 10fps for almost all occasions....5fps only in very good seeing. There's not been anything resembling very good seeing in Brisbane for quite a while. So 10fps it is.
I never shoot at 15fps with a ToUcam. Too much compression
Also...dont worry about rotation with Saturn. Unless you know there's going to be a storm visible...you can go to town (within reason) on capture time.
I capture for between 2 and 3 minutes (for a total of between 1200 and 1800 frames respectively)...and as Mike says, 2000 is far too many frames to stack. I generally stack around the 400-500 mark...if the seeing's OK. But I also set the % quality in Registax around the 85-90% mark...to kill off the crap frames in variable seeing.
Cheers.