Short version is I did not cut the one-hole groups that the initial ladder pictures above indicated I might...
I had some scope adjustments between each group to get to the POI I needed for my hunting sight-in, but those should not have had that great of an impact on my groups.
So I shot three 3-shot groups at 100 yards with the 63/RL-15.5 charge under the 225 AB. 3.38" OAL (still a big jump to the lands) and CCI200. Rifle is a 35 Whelen AI. Temps were 66-79 F.
I missed three chrono readings, so with n=6 the speed was 2716 FPS with an SD of 5.
Groups were 2.11, 1.11, and 2.01"
I may have been shooting a bit poorly, but it didn't really feel that way. I'll take this as the back-up to my 9.3x62 on my upcoming elk hunt.

I'm really looking forward to trying more of the RL-15.5 with the 155 Scenar in the 30-06. That is showing a lot of promise in the one trial I made with it so far.

Cheers,
Rex