Wales caps at 20

I recently learned that the Welsh devolved government are planning to set their default road speed limit to 20mph. I don't think this is a good idea. When I'm driving on a level road at 30mph, I can change my gear lever up to 4th gear; when I do that, my car rev counter dips to 1500 rpm. In third gear it is spinning at 2000 rpm. Higher gears slow down the engine. If I drive 1km in 3rd gear I would burn more fuel than if I was going in 1km in 4th gear. I can't get to 4th gear on any terrain at 20mph, my engine doesn't produce enough pressure to pull it off. My car needs to be moving at 30mph. 

My car and many other manual gear transmission cars like mine get more fuel efficient as they build up speed until about 65mph, after 68 it starts going down again. Let's just wait till most cars are electric.