The majority of smokeless 45s are using a 1-22 and well proven with current bullets. It should likely still work well with conventional bullet upto 240-260gr such as the PRs and monolithics upto around 220gr or a bit more. The PRs are only limited by the soft lead which will deform in flight if shot too fast. A plated/bonded or jacketed 40 in that range wouldn't have those limits. Doc actually did have some PowerStar sabots shooting soft lead 350gr bulllets IIRC in the 1-20s in the 1600fps range.
They may sound slow but run it through a calculator out to 250 yards sometime with his advertised BC.
1-24 would be a interesting twist for current bullets and higher speeds. It should still be fast enough for some sabotless weights and conicals. Maybe not as heavy as the White conicals but close.
1-22 would be the easiest for testing since its a common twist offered by many barrel makers. It works with current sabotted bullets from 1900fps-3000fps. BH209 speeds can approach the middle of that number so IMO its a good place to start. It also works with sabotless bullets from 250-325gr in the 2200-2600fps+ range. BH209 has also been tested sabotless with this twist with loads over 120grV with reasonable success if you get the correct bullet to bore fit. Even Bob Parker had one made and was shooting a sabotless 250gr well over 2000fps IIRC with 110grV BH209.
Pressures are surprising low with BH209 sabotless too. Swinglock shot a sabotless 350gr with 84grW and got about 2000fps but he used a 1-18 twist since it was a dedicated sabotless gun. The test barrel showed well under 28k psi with that load. He also wanted to use mainly bullets offered for the 458 class of guns which tend to be heavier.
Knight's target rifle in 45cal (DE658) from the 2006 catalog also used that twist with big conicals for most of its wins at Friendship. IMO that twist would be more dedicated to a single purpose and less flexible with subs. At least until some really heavy bullets are available and new longer sabots to handle them.
Personally i would like to see a 1-24 only because its different and will be fine with current bullet options. It will also give a good chance for success if newer bullets become available. 1-20 still has a bad rep even if it was only due to flawed advertising and older sabot polymers. If you want to encourage the SML crowd to try Knight 45s, a 1-22 would probably have the best chance.