Layne Simpson wrote a piece on this round, as did IIRC, Bob Milek- though in handguns.
No doubt the 85 PT is a good bullet, for small capacity rounds, but at these speeds, I would trust a plain CC 85 BTHP GK, as they will expand great, and hold together fairly well. I think the GK will give a bit larger wound channel than the PT, and in this smallish 6 bore, that is welcome. You should have seen the hole in the deer my son shot at 300 yds with an 1885 LW in 243.......DRT. A second had it's on shoulder busted and went about 60 yds. I would stay in a middle range of weights, and construction if me.
FWIW, I dropped a south Tx deer with a 70 TNT from a 6BR around 200 yds, shredded both lungs, went about 50-60 yds. I shot behind the shoulder as you can imagine. But if you hit bone, it will most likely fail to go deep to vitals and disappoint.....
Enjoy your new custom and much success afield. I ran a 6TCU in a TC Carbine, 21" - 10 twist IIRC, might have been an ROT of 12 if it was not 10. I had about 5/8" groups with the GK. H335 IIRC.
