I'd not use anything tighter than 18" IF I had a choice. I do not believe faster is necessary - perhaps is shooting 750gr. bullets in a .45.

My current 18" .458 GM barrel is putting jacketed 405's into 7/8" (10 shot witnessed group) at 100 meters with aperture sights front and rear and 525 FB cast bullets into from 1" to 1 3/8" with same sights and black powder - witnessed. With hard, gas checked 505's and Benchmark powder, it's running 1 1/2" merely using the Sharps open sights at 100 meters off bags - also witnessed.

So - if 24" is all that's needed according to some of the best big game shooters and gunsmiths, why go any faster than needed?

As far as longer range stability is concerned, some years ago, the Quigly offhand match (Rendezvous BC2008?)) at 750yards was won by a fellow shooting an original Trapdoor Springfield using 525gr. Lyman # 457125 bullets - that rifle had a 22" twist & his accuracy proved the stability of the long bullets in what some think of as too-slow a twist. We also know these calibers, bullets and twists used to shoot right through a buffalo, but in the longer cased rounds 18" seemed to be preferred - at least for shooting in 1,000yard competitions.

The faster the bullet, the more easily it is stabilized in a given rate of twist.

Thus, a smokeless powder round, running 600 to 800fps faster, in the same twist, is even better stabilized- why increase the rate of twist further yet?
Faster the twist, the higher the pressure and slower the bullet - IF all else is equal - in theory.