When I was young, I drove way too fast, Now everyone says I drive way too slow. When you get older, for some reason, you want to live a lot longer.
I try to keep within in 10 mph of the posted limit. There are a ton of speed cameras in Maryland and they are set at 11 mph above the limit, BUT on an interstate, the ‘flow of traffic’ may be much higher than 10 over the limit. Going at the posted limit on an interstate may actually make you a hazzard to other drivers. You may be driving at 65 in a 55 posted zone, but there will be huge semi trucks tailgating you along the way.
In Georgia, the state is considering making it ILLEGAL to drive BELOW the speed limit in the left lane (aka passing lane). I hardly ever see anyone driving at the speed limit (except on a rainy or snowy day), and it really is a huge hazzard to drive below the limit.