You just made my point for me. I'm a civil engineer, with experience in highway construction (want to take a guess where?).
The NJ Turnpike mainline roadway happens to have 12' wide lanes, 12'+ wide shoulders on both sides of the roadway (except at certain overpasses), generally low grades of 1.0% or less, and relatively few curves sightlines of over one mile on straights. In dry conditions and light- to moderate-traffic, this high level of service leads to a design speed in the vicinity of 100 mph. With a posted LIMIT, as a general rule you should be establishing a speed that approximately 85% of motorists can safely maintain and stop from if necessary. By simple calculation, a posted speed limit of 85 mph (as on the Texas tolled highway) can easily be justified.
The high number of lanes compared to most highways/interstates and separation of cars from trucks/buses on approximately half of the NJ Turnpike also works to safely spread out vehicular traffic, to the point where natural off-peak hour traffic volumes travelling at 90 mph for cars and 80 mph for trucks are not uncommon.
As a experienced, focused driver (no cell-phones, conversations, yelling passengers) in my sports car, I can and may have safely maintained/stopped from triple digits as needed.
This may seem off-topic, but as long as we're talking both speed limits and guns the point is this: I don't agree with limiting the rights of law-abiding, otherwise capable individuals to satisfy a group's misdirected calls for increased perceived safety. Personal responsibility and proper training are the keys here.