Out of interest, how well is the speed limit in somewhere like Montana policed? Do the cops actually pull people for doing 1mph over the current limit?
I tried to get an answer to that question and was met with the usual barrage of answers...it seems to be handled on a state-by-state basis but there isn't a resource I could find that laid things out in a simple manner. Here in Oregon I've always understood that there's a 7 MPH margin of error, from inaccuracies in both the radar units and cars' speedometers; not sure where I picked that up from though...don't think it was in the driver's handbook.
Anyway my SOP is to chance about 5 MPH over the posted limit; it's worked for me for 25 years, and I'm certainly going a heckuva lot slower than the army of maniacs out on the road. But then I don't do much in the way of traveling so perhaps there are states where the limits are enforced for real.