I personally use Reloader 15 @ 87 grains plus backer rod filler, 89 grains is the RL15 load out of Wright’s book, & slightly less recoil than 4831 loads. Have not tried the Reloader 19 loads.
Your estimated loads sound about right for starting loads and work up to regulation.

Wright’s book, 3rd Edition, page 103 gives “average regulating loads” and the attained feet per second. The bottom of page paragraph mentions that the 500/.450 3-1/4” loads around 2000’/sec regulate at what seems to be the equivalent of the tropical 70 Cordite load in several different rifles.

You did not mention the weight of your Hollis, my Scott is 10 1/2 lbs.
- Mike