It seems to me that drivers who are proven to be safe, good drivers who are fully capable of safely driving at higher speeds should not be limited to a unnecessarily low speed limit. A road could have multiple speed limit signs, perhaps color coded by certification level, or maybe just have the lowest
speed posted, and let the qualified drivers exceed that speed by a certain amount.
People would be certified by taking more rigorous written and driving tests and it could be indicated on their license. To indicate their certification level to police, bumper stickers, special license plates, or small radio transmitters could be used. They would probably have to be recertified periodically.
There could be one level of "expert" driver, or perhaps multiple levels. An expert might be certified to drive at the normal limit +10 MPH, so in a 55 zone they could drive 65. This could be posted or just implied.
Obviously, this has the potential to cause problems, with an even greater speed gradient between the cars on the road. There should be harsher penalties for unsafe driving, weaving through traffic, tailgailing, etc. for expert drivers, because they would supposedly be good drivers that should know better. Likewise, perhaps if an "expert" is caught speeding above their certified range, they would be penalized as if they were not certified at all. For example, if someone certified for limit +10 MPH was caught doing 80 in a 55, they would be penalized for 25 over, as opposed to 15 over, again because they should know better than to speed, and because their certified speed should be "enough". Then again, maybe not, because you could easily accidently be doing 70 when you meant to be doing 65 in a 55, and suddenly get stuck with a ticket for doing 15 over when in reality you weren't much over your certified speed.