Model 1892 in 25-20 rebarrel project|General Discussions & Questions|Forum|Winchester Collector

I have finally decided to upgrade/ improve my favorite shooter. The current 24” barrel is at best in fair condition but is very accurate using jacketed Remington .257”, 86 grain bullets that are currently out of production. I have tried many loads using .258”, 85 grain cast bullets and cannot get near the same accuracy as with the Remington bullets. 
I am looking at a Hunter brand replacement barrel but there are many options:

 5 or 6 groove rifling

single point or broached rifling

barrel length (would it help accuracy at 100 yards to longer than 24”?)

rate of twist

Does as anyone have experience with cast bullets with the above options? I would like to choose the best option for exclusively shooting cast bullets.

https://www.mikehunterrestorations.com/barrels.html