That caliber has a reputation of being a killer but if you read Korean war books like "Break Out" or SLAM's "River and the Gauntlet" there were a lot of Marines getting shot with a PPSH 41 and keep right on fighting for hours and days.
The bullet is really light if I'm not mistaken. The commies used their 7.62XX25 to give people "9mm headaches". If I had a choice between a MP38/40 or a PPSH, it would be a hard choice. I'd probably go for 71 rounds instead of 30/40.