Road safety, fuel economy and mental health would be improved.
The 40 mph limit for goods vehicles is outdated – They have air-brakes now and with disc brakes using ABS, EBS and some have engine brakes and retarders.
There is also an environmental issue here as you are not quite able to achieve top gear at 40 mph. Raising it to 45 mph would save fuel and reduce the frustration of the following car drivers as their speedo's would read 50 mph.
It would also stop/ reduce the crazy overtaking manoeuvres.