The 1-18¾" twist shouldn't be a problem with RN bullets, the 250gr BTB will stabilze to 100yds in a 357Max, dunno about further, the added velocity should work out to 200yds in the 358W, but the only way we'll know for sure is if someone tries it.
I was told, and read that the 1:16" twist in my RMEF 35 Whelen wouldn't stabilize 250gr spitzer bullets, but the <1" groups it shoots with the 250gr Speer spitzer tells me different.
Mattparliament's 35 Whelen shoots bug hole groups with the 225gr TSX, not a short bullet, it's longer than the 250gr Speer.
Tim