Shooting resolution equals maximum output resolution, yes. One thought might be to use a decent upscaler like Red Giant to make your footage ‘higher rez’ (quotes becuase it’ll still just be software magic, not real resolution) and then stabilize. Or get creative with layering, or bordering, to mitigate the inevitable frame movement on the edge of the image.
Though the camera thing makes me wonder, though I’ve never tried it, about using a wide angle focal length on your virtual camera and placing it ‘close’ to the stabilized precomp – that might be an interesting way to fudge the edges with lens effect instead of ugly black triangles moving around…
Yes a pickle, but those are delicious sometimes.