Canon Fodder the speed limit is the highest you are legally allowed to go, if you are concerned about the wind or money then go slower, simple.
Renagade going over 100mph is perfectly safe in some cars with some drivers in certain road and weather conditions. Also not sure why you care about getting rid of the average speed cameras, they are by far the best way to guarantee a given speed over a given stretch of road.
Germany have numerous roads with no speed limit (about half the motorways in Germany are restricted to 81mph/130kph). However I also believe that in general, based on the driving I have done there, the average quality of car there is higher than ours not just more high end cars BMW, Mercs, Porsche, etc but much less old bangers. Which could also influence their safety record.
The problem with 80 for us is that using the standard police rules is that if the limit is 80 then most police forces have a 10% or 10% + 2 rule. So 88 or 90 would be within tolerance of the actual limit. I think modern cars and road surfaces are perfectly safe doing more than this however the problem comes with complacency e.g. we could safely do 80mph in all conditions. Obviously doing that sort of speed in heavy rain with low visibility at night is a bad idea. I would be happy with a similar system to the Germans of unlimited but monitored so that if conditions were not within a certain range a speed limit was applied. Then speed cameras on most signs to force drivers to comply when a speed limit is needed.