i feel this is important as sometimes there are too many people going slow on a motorway and this then causing accidents instead of people speeding and also would be able to direct police to more important crimes other than motorway speeding!
The 3rd lane should be above 70mph as same with the middle lane, so that you can have it set out as…
1st lane 70mph
2nd lane 70mph-90mph
3rd lane 90mph+
or just have it set like the autoban in Germany where its unrestricted and trust the moterists to use commen sense, the idea of leaving the 1st lane at 70mph is there are some people that do not like change or to go faster so this way would then suit all motorists.