The old Alliant catalog lists 6.0grn Green Dot as the max for .357mag with a 158 LSWC and with a 180 JFP, and 5.0 as max for a 200 LRN. It lists 3.5 max for a 158 LSWC, 3.4 max for a 160 JSP, and 3.1 max for a 200 LRN in 38spcl cases - bumping to ~3.7-3.8 max for the 158/160 class in 357mag cases, only operating under 16kpsi. The .38spcl+P data with a 17kpsi max shows 3.7grn for a 158 LSWC and 3.2grn for a 200 LRN - again, scaling somewhere around 3.5 for the 200 and 4.0 for the 158 if loaded in a 357mag case...
So at 4.5 grn under a 170 cast in a 357mag case, he was over 17kpsi 38spcl+P standards by about 3/4 grain, and likely falling about the same 3/4 grain under a predicted max for a 34kpsi standard. Likely cooking somewhere around 24-28kpsi. Not a max pressure load, but certainly not a low pressure load either. Based on the data, I’d guess it would have been trucking around 850, maybe just under 900fps from a 6” barrel. A little faster than a typical 158 +P load, and touting a bit more bullet weight. Not a max load, but not a load I would want to stand in front of.
Stopping a bullet in a 2x4 isn’t so surprising, however. I’ve caught hundreds of 45acp 225-230grn slugs, full power loads, in 2x4’s. I caught end cut scrap from my brother’s construction job when I was in college, stood them on fence rails and used them for bowling pin match practice. They’d catch the bullet more often than not. The same loads which would easily flatten a bad guy or a buck. I’d catch 115-124 class 9mm slugs in double layered 2x4’s regularly also - speed makes a big difference.