Best fullscreen dimensions

Morning people!

Got a bit of an interesting question here, and I don’t know quite how to word it for the search bar.
Part of my job entails me making full screen flash animations for use on Digital Billboards. We’ve built a browser based software package that pretty much just drops the flash into chrome and tells it to go fullscreen.

Most of our clients run 16:9 HD screens, generally 1920x1080.

The hardest thing i’ve found with it so far is optimizing my campaigns to run on (lets be honest) **** hardware. Little Viewsonic 1ghz atoms is what most people end up choosing to run these with, it fills me with sadness, and anger, and then sadness again.
So far i’ve found that making the stage smaller in flash, 800x449 to keep in perspective, seems to work well… But then the images inside need to stretch out, and i’ve got to use ‘allow smoothing’ to make it look nice. Of course, this then hinders performance.

So does anyone know, is it better for me to be building the campaigns in 1920x1080 to start with, or keep up with the small stage to scale up approach? Is this the better way to go to keep frame rates up, or am I just hurting my own product by thinking its the ticket? Does flash draw extra resources just to scale itself?

Cheers if anyone can help me with my convoluted question…