Honestly, fuck radar detectors and all that jazz. It is all about smart driving. I can usually drive 75-80+ on all trips just because I stay alert and drive smart.
Drive with a car in front of you and back who want to do the same speed you do, if not one or the other. That way, you only need to worry about looking towards the front or rear for police, because in most cases if someone is behind you they will get busted from cop in rear, cop from front, car in front.
Also, I just watch brake lights and oncoming traffic.
I used to have a radar detector and it just made me lazy and not alert. The reliability is too far off for me to rely on one heavily.
Then, if I don't feel like paying that close attention when driving (as in to brake lights up ahead and all that jazz) I just do 5-7 over.
Has worked for me fine. *knock on wood*