It’s been awhile but I have been shot with a handful of Tippman paintguns at various ranges, from 30 meters to point blank.
These were with standard paintballs, which are definitely not solid affairs. With a modest bit of hand strength, you can crush a paintball. You can easily crush one with your molars. It is trivial to stomp one and make it “pop” audibly and squirt paint some distance. So they’re not especially solid is what I’m trying to get at.
At moderate ranges, I was getting welts on exposed skin with these paint shots, and pretty livid bruises through thin summer clothes. You know when you’ve been shot if you don’t have thick clothes, I tell you what. At very close ranges, lots of swelling and some bleeding, enough energy to put a hole through thin cloth. At the back of the head at very close range (the shooter was a coward who never confessed) I was basically stunned and lay prostrate for a half-minute with a bleeding, swollen head wound. Not at all unconscious, but very acutely aware of how much the back of my head hurt.
These paint shots can easily put out an eye without adequate protection. A solid shot with that much energy runs the risk of being lethal I’d guess.
A solid shot at 250 feet per second is capable of, I’d guess, really serious injury.
When I got smarter, I started wearing an old longcoat as protection. (This was pre-Matrix, give me a break.) Loose-fitting, thick clothing can greatly reduce the effectiveness of paint shot. Looser, thicker clothing or (B)MX-style armour would probably work quite well against the solid stuff.
Editted to add: 250 feet per second is standard velocity, and you can find some places that go up to 300. So this is about as standard as it gets.