I get the same thing around here ...
I usually maintain my speed to be about 20-25% over the speed limit, though, in construction, or school zones, I'm more conservative with my speed.
My commute from work to home, has much 35mph, and some 40mph, 45mph, and 50mph sections.
In the 35mph zones, I'll keep it under 45mph, but will get passed by quite a few people.
The same road, the speed limit picks up to 45, and I try to increase my speed by 12mph... but pretty much almost never seem to stay over 50mph, because there's just toooo many cars going slow, in both lanes..... for no known reason.
Also I hate those people that go 35 in the 45 zone, then speed up to like 50, then slowly slow down to like 30 .... during a long stretch of open road with no passing, and speed limits varrying between 45 and 50 the whole time ....
Also, when the speed limit says 55, don't spend 25 years accelerating from 45 to 55mph .... just press down on the gas already!!!!!!!!!!!!
And, worst of all, are those people who ride in the left lane, when they are not passing anybody. Just because they are lazy or stupid.