Well, turns out the problem was that all the tiny "fins" I had on the outside of the pods to simulate the strap-on holding mechanisms was really messing with the drag coefficient, which was up around 300
Cd override was set to 0.80, and the results look much more respectable!
Flights look fairly nice on black powder, especially the (2x) B6-2 and E9-4 (though an E9-5 would give a bit better Dv's, 4.5 would be even better) flight, which clears a 36" rod, stages at about 80-100 feet, and stays under 1000. This ought to really fly even nicer with high-thrust A's or B's in the pods for demo flights.
[2] B6-2 -> E9-4 ..... 992' ..... Dv 18.7 ft/s ..... 3/16" x 36"
[2] C6-3 -> E9-
5 ..... 1196' ..... Dv 2.4 ft/s ..... 3/16" x 36"
[2] D10-3 -> F12-5 ..... 1735' ..... Dv 9.1 ft/s ..... 3/16" x 36"
Now I need to find time to build it! I've always liked parallel-staged designs, but I've never built one before, just read reviews of kits and diagrams of how they work.
(It turns out those strange ring things in the base view were artifacts of the centering rings inside the pods. I removed the rings for now, since they hardly add any weight, and aren't hard to add back in [rear ring is a double-layered piece of fiber, 0.1" thick, forward ring is standard 0.05"].)