This is exactly what I have been doing the last 2 weeks.
I upgraded from my z2 to the Sony Pearl. I haven't got around to mounting my Panamorph U-100 that I had been using with the Z2. I have watched Spiderman 2 and Sgt. Pepper's (both 2.35...save your SP comments for another thread) and zoomed/shifted the Pearl. I'm effectively getting 1920 X 720 in this mode.
PQ is better than the Z2/Panamorph combo...whether this is the extra resolution, SXRD reducing pixel structure, or just a better projector...I'm not sure. The only thing that I have noticed that annoys me is that it seems the letterboxing bars are affecting the dynamic iris. 1/3 of the panel is black, so the iris adjusts accordingly.
I'm going to give the Panamorph a shot with this setup, and it's going to be used like I always have used it: for scope movies only, slid out of the way for everything else. The only problem I can see is that the Pearl lens is huge compared to the Z2. I'm not sure if the U-100 has a big enough opening to accept the light path from the lens. A quick hand-held test makes it a 50/50 proposition. I have to mount the Pearl back about 5-6 feet for the throw ratio to be correct, which is why I haven't bothered trying it out yet.
Reader's Digest version: going from 720p+Panamorph=<1080p zooming. 1080p+panamorph=?