Stephen,
Lyman shows Plus P loads one or even two tenths of a grain of powder heavier, from 'normal' working pressures of 16000 cup range: plus P is 17,600, or 18,200. This is far short of the 22,400 set by SAAMI. After looking at your link, I have to wonder if any manufacturer is making real plus P.
Hornday ammo has a adverstised 38 special load of 850 fps with the 158. If I recall from your link, (and I may not correctly) Plus P was something like 866 fps. Well, bowl me over! We should drop the Plus P designation, and call it 38 Luke, for lukewarm, or maybe just Plus pp, for paritally plus (and something else)
Alan Fud- Despite the whimpy loadings of plus P, the 38 Special does not have a bad reputation, particularly with the heavier bullets.
munk