American Handgunner, Jan/Feb 1998
+p vs. standard catridge (2" S&W 442)
110-gr. std. 722 fps. 3.6/ft. lbs. recoil
110-gr. +p 891 fps 5.2 ft. lbs. recoil
They say tt is an 18.9% velocity increase with a 30.8% recoil increase.
The article says +p is better in .38 Special because maufacturers have spent so much time designing good bullets around the higher pressures.
FWIW, from handgunsmag.com I have also some ballistic data for .38 Special loads from a 2" snubby. Shots were fired into bare and clothed gelatin. Briefly, the averages:
Fed. +p 129-gr HS -- 810 fps, 13.64" penetration, .48" expansion
Fed. +p 129-gr. Nyclad -- 874 fps, 9.3, .69
Fed. +p 158-gr. Nyclad -- 760 fps, 19, .37 (i.e. none)
Winch. +p 158-gr. LSWCHP -- 821 fps, 16.2, .44
Winch. +p 125-gr. SJHP -- 723 fps, 16.5, .42
Winch. +p 125-gr. Silvertip -- 726 fps, 13.1, .55
Winch. +p 130gr. SXT personal protection -- 825 fps, 14.6, .56
Speer +p 125-gr. GDHP -- 823 fps, 13.4, .60
Remington +p 125-gr. Golden Saber -- 824, 10.9, .53
Based on pure numbers, the Winch. Personal Protection and the Speer Gold Dot look good. I carry the heavy Winchester load -- I just shot it yesterday at the range (along with some Golden Sabers). The heavier round just "feels good" to me out of my S&W 642 Airweight.