When you neck down from these larger cases, necks get thick and tapered. These two issues can leade to a lot of issues in terms of consistent neck tension, run out, doughnuts. As you do down in caliber, smaller variances in neck tension mean more trouble with groups.
I mention this because I don't want you to have the blinders on when you go down this road.
As the brass thickens, you can fudge a little by using bushing dies vs std dies.
The 20 Practical is an easy route to go, but You would want a large case for a 55g bullet more than likely. I don't know what a 20 tactical or a 204 Ruger would do with a 55g. I have not seen Winchester brass for a while, and my pile is dwindling. I went 22/204 and 6mm 204 with amazing results in both, but neither has the down-range ballistics of the 55g 20 caliber.
A 20-250 AI or a 20 Creed is where I would be to utilize the long-range ballistics of a 55g Berger, nothing less.
Expect 800 rounds of barrel life in the 20-250 AI with a barrel that looks like a sewer pipe at that point.
BR cases using AIC mags will work, but a 22x47 Lapua would save you a ton of grief if that is all the horsepower you will want. K&M neck turner with the carbide cutter to remove doughnuts should be on your list of things to buy. If you do not want to turn necks or deal with doughnuts, you may want to re think the project.