I'm guessing, at geographic-feature altitudes, the baseline needs to be larger than the aircraft by such a significant factor that time, speed, and direction need to be part of the equations. In other words, one camera, two photos, with a precise known time and speed between the two photos.

Of course, it will be possible to get the baselines too far apart, at which point your image detection algorithm starts to return nothing but noise. I think that's your noise floor: The more dissimilar the two camera photos, the more random the resulting 3D data set. Your optimum baseline will be, I'll bet, a function of the camera's resolution, the size of the geographic features being captured, and the camera's distance from those features.