Most of my work is large format, but this is about twice as many pixels as the largest wall I've done. I'm curious to hear how you get along with it!
If you were doing slideshows on gigapixel photographs, I'd want to do that part in WATCHOUT instead of Ae.
For Ae work, I'd suggest that "resolution" means "sharpness" to the viewer. If you are designing computationally expensive soft, organic or out-of-focus backgrounds, you can design and pre-render those elements at half- or even quarter-res and scale them up in the final composite as long as there are a few tack-sharp full-res elements in the foreground to establish the "sharpness" of the display.
(As an aside, high-res work is a great example of how improving Ae's performance could open up all kinds of new creative possibilities.)
w.