Dave, I also have a Custom "75 Shadow" and a fully worked 75B with all the goodies.
For most of my shooting, they both shoot well for me, but each has some minor advantages.
I didn't buy the SPO1 Shadow ( my son has one) because the front end is a little heavy for me when swinging through spread out targets. Mine had some added weight from .55 bbl but no rail. I still swing through targets a little easier with my B. Straight ahead shots are faster with my Shadow.
I did a take-off on your dot drills Tuesday at six yards. Purpose was to see and stop trigger finger pushes to the left when shooting fast. I wanted two shots per second Plus the draw and sight time, so I set par at 5.5 seconds.
On a USPSA target, I ran 2" wide masking tape vertically from shoulder to bottom, neck to bottom and from the other shoulder to the bottom. I put four 2" red stick-ons equally spaced on each verticle strip of masking tape. Draw and shoot starting at the bottom stick-on and shoot ONE shot at each stick-on going up, then shoot back down the strip of tape shooting once at each circle: 8 shots per strip. Going down was the killer because you can't see them until the muzzle clears-so timing was used going down.
My MAIN point was to get all the shots on the two inch masking tape without pushing any left. Hitting the circles was a plus. The results were interesting . on the draw, I hit or came very close to the bottom circle every time. The two middle circles I only hit a couple of times each. I hit the top circle almost as good as the bottom (transitioning from up to back down the tape strip) . I shot twice per second pretty steadily but had a tendency to speed up on the middle dots to beat the timer buzzer. I ran over once.
First run was a litlle awkward, and I did push two of the eight shots a couple of inches left of the tape and one just a little left. Concentrated on the grip for the draw, especially the weak hand , and I pushed two more left, but just outside the tape. Third run I was on the tape for all the shots. I did go left just a little 3 more times and went right twice on several more runs, but I showed some improvement. I alternated shooting this drill with 5 plates and a stop popper at 10 yards. Concentrating on my grip helped keep the shots closer to centered on the plates.
I'll try it again next week shooting rows left to right and back. Cool drill, thanks for the idea..