I believe that 70mph is the speed limit on dual carriageways. As long as you are not a hazard to others then you travel at the speed you are happy with.
If 70mph is a must during your motorcycle test how can the goverment justify the 30mph limits for 50cc motorbikes and scooters?!
These are allowed to use dual carrageways. HGV's are governed to 56mph max and only allowed to 40mph on unrestricted single carragways.