Much of this will be similar to my answer to your other question:
Compositing is faster, by far. On the iPhone, content is drawn into a CALayer (or into a UIView's backing CALayer) using Quartz drawing calls or from a bitmapped image. This layer is then rasterized and effectively cached as an OpenGL texture on the GPU.
This drawing and caching operation is very expensive, but once the layer is on the GPU, it can be moved around, scaled, rotated, etc. in a hardware-accelerated manner. All the GPU has to do while the layer is animating is to composite it with the other onscreen layers every frame. This is why Core Animation can do 50 layers animating around the screen at 60 FPS on even the oldest iPhone models.
Layers and views only redraw themselves when prompted, or if resized when their needsDisplayOnBoundsChange property is set to YES. The drawing system is set up this way because of how expensive it is to redraw and recache the layer contents. If you can, avoid redrawing your layer content regularly, but instead split it into layers or views that you can animate around individually using Core Animation. If you need to animate a changing shape, look to CAShapeLayer, which makes this much more efficient than simply redrawing every frame.
As a worst case, yes, you can take the portions of your view that are static and move them to one view, then have a subview which has only the changing portion of your drawing within it. Performance won't be great, but it will be much better than if you had to redraw everything within the view. Compositing overhead will be negligible compared to the expense of drawing.
