I run a 158-grain lead SWC over 5.0 grains of Titegroup as a Magnum target load!
It's not full bore Magnum power. According to Hodgdon's Cowboy bullet loading charts with a 158gr LSWC it is nominally 1108 fps and 24.9Kcup in Magnum brass. In a shorter 38 Spl case pressure would be a good bit higher than that. My unscientific seat-of-pants-o-meter tells me it would be probably no more than 30,000 CUP- and that's about double a run-of-the-mill 38 Special...!
The SAAMI limit for 38 spl +P used to be 20,000cup but they reduced to 18,500cup 'recently'. Hodgdon still shows loads which are over 18.5k but under 20K as +P loads, and I personally have no problems using the 20K specification in guns which are of sufficient durability- such as nearly any major-brand 6-shot steel revolver.
What I typically load for 38 special is 3.5 grains of Titegroup under a 158-gr lead SWC. That in theory hits (approximately)860 fps & 13.5K cup by averaging Hodgdon's Cowboy lead load data charts for Titegroup- which shows 3.2gr start and 3.8gr max loads.
This is my preferred 38 special load!
I also load a 158-grain Speer Gold Dot over 4.0 grains of Titegroup as a 'hunting' load. Performance of these was similar to other factory personal-defense/hunting loads I fired. It's a 0.1 grain overmax for a non+P loading, but...I find it shoots well even in older Colts and it *is* under +p by a couple tenths of a grain.
I am sure that Mr. Pearce developed his loads to suit his gun- an oversized "N"-frame S&W which was designed for the 44 magnums- and were I shooting them out of that sort of gun I would think they would be OK. I would NOT shoot them in anything smaller.