There's an interesting article on the subject in HANDLOADER #27 (1970) by Neal Knox and George Nonte. A number of then-contemporary hot and very hot .38 Special handloads and factory ammo were pressure tested.

Hottest factory load was the Norma 110 grain JHP at just over 27,000 psi with a 1,200 fps muzzle velocity from a 4" S&W Model 19. There is a handload listed using 8.1 grains Unique with the 110 grain Super Vel JHP bullet; just over 21,000 psi with a muzzle velocity a bit under 1,200 fps from the same revolver. Such loads probably wouldn't and shouldn't even bear consideration today from safety-conscious handloaders. Components likely have changed in their makeup and pressure measuring equipment surely has seen improvements in precision during the past four decades.

As a side note, anyone who has used Super Vel .38 bullets is probably aware they were undersized, presumably to lower pressure. I don't know about jacketed bullets from other makers.