If you hit a pedestrian going 35 on a 25 mph neighborhood street, the majority of the time, that pedestrian will die. Probably closer to like 70% if you're driving a truck. Going 10 over in pedestrian areas kills people.
In residential I tend to go around 15-20 instead of the posted 25. I'm almost never in a hurry. I drive a 20 year old 2 seater convertible sports car, not a truck.
I was talking about highways. Posted speeds are 65 for the vast majority of them. Many are 5 lanes in each direction. If you go 65, you will be passed by 99% of traffic, including semi trucks. Most traffic is going 75-80mph and it's not uncommon to have the entire freeway cruising around there. At 65, you may be following the law, but you become an obstacle. I've been on highways on Sundays where traffic is flowing almost at 90mph. And I don't mean a few cars weaving, I mean almost everyone.