Thanks for all the comments and suggestions.
The RST shells are their "2 1/2" load, 20 ga. 7/8 oz 7.5s at 1150fps with a plastic wad. I finally had a chance to pattern some of my reloads as a comparison. They threw 74% patterns (68-76% variation), which is significantly tighter than the RST shells. (The reloads were WinAA+Win209+15gr. Unique+CB1078+.875oz of Magnum 8s). I guess this is just another example of different guns liking different loads.
Patterning may not be a perfect science, but I would prefer to have some imperfect information than none, as long as you understand its limitations. I use the method that Oberfell&Thompson set out in their Mysteries of Shotgun Patterns (efficiency, distribution and "patchiness" based on the number of 5" gaps). In this case, I used 5 patterns because this gun is an upland game gun and I didn't need 10 patterns to figure out if the gun was close to what I had specified.
I played around with the Optimizer program Dr. A.C. Jones has on his website to determine the best pattern efficiency for what I wanted to do - in this case, the program determined that to get a 90% probability of at least 2 pellet strikes, the density had to be at least 80%. So I asked to have the chokes set at 80% for 20 and 30 yards, which should equate to something close to Cyl and Mod. Interestingly, the bottom barrel patterned at 74% with the RSTs at 20 yards, which is a bit more open than Cyl (?).
I also shot 5 POA patterns which were right on the money. I learned the hard way to NEVER shoot POI patterns if your gun shoots good POA patterns.
