Dodgepong, I'm curious about this; do you mean bandwidth issues, or..?
I've found that if using a 1080p base resolution, running the c920 in 1080p mode and letting the Lanczos downscale do its thing results in better picture clarity than running at 720p, stretching it larger, then downscaling again, if you use a fullscreen-cam at all.
And setting it as a global source doesn't allow it to be run at different resolutions in different scenes, so... kind of stuck re-sizing it down from 1080p to fit any scene in which it's used.
On a side-note, does anyone know if the chromakey is done before or after any re-scaling? Does the rescale preserve the alpha layer in an anti-aliased manner? Seems like it may not, with how pixellated the edges get.