Carpe, oddly enough, I never asked JD what twist I had. He told me initially to use 240/250 HPBTs. They worked, then he encouraged me to use/test other bullets. My SSK barrel shoots everything great from the 240/250 HPBTs to the 170/186 gr. Lehigh fracturing HPs. I also tested a bunch of other bullets for Lehigh with different weights/shapes that shot great, but performed poorly.
Recently a friend gave me some Horn. 200 gr. RNs with a flex tip or whatever. They shot about a foot higher than all my other loads, so I'll not be testing them.
The 220 HPBTs shot well in my gun. The first 2 deer I shot with them at 200 yds. kept on feeding for 4-5 minutes then dropped. They hit exactly where I aimed. I, too assume my barrel is a 1:8.
I don't know if this will translate to the .32-20 sub, but my bullet preference for the Whisper is:
1) 220 Sier. RN (cheap, accurate, deadly)
2) 186 Lehigh fracturing HP (expensive, extremely deadly- 80-90% instant drops/kills)
3) 250 Sierra HPBT Match- not made, but longer than 240, more unstable, tumbles great, kills very well (JD gave me a bunch).
I use these 3 about all the time.