I'm working on an installation that uses after effects to project animations onto a print in a gallery and finding that configuring the composition size to the size of the canvas print is making AE run really REALLY slowly. The print is 12000x18000 pixels @300 ppi (40in x 60in). I guess it just occurred to me that I need to find out if composition size should be configured to the size at which I would like the image to be projected or some scaled down ratio thereof. Will I lose a ton of resolution (using a high resolution projector) if I scale my image down a bit? Help?!
So you're working on a video that will be projected? or a comp that will eventually be printed?
If it is the former, then your approach is flawed. You should find out the video resolution of your projector (1080HD, 720HD, standard def) and then use black solids to mask portions of your frame if needed to match the 2:3 aspect ratio. Far more manageable since you'll be limited by the projector.