Photomerge is fickle, it'll spit out crap results if you're not militant about your sequences. If just one shot is an outlier, the perspective gets all screwed. Of the different layout modes, Cylindrical seemed to work the best. Beware you'll need a ton of RAM, and a bit of patience. Also, best to experiment with downsized…
Here's a little extra info on a quick process and setup for how I do screens. Firstly, I place the camera in the scene. I open kismet with the camera selected and make a new Matinee. Matinee will usually give your camera a movement and a FOV track. I usually kill the movement track because sometimes the first keyframe…