The speed limit is the maximum you should go- whilst I agree crawling about at 20mph in a 30mph zone is likely to cause issues- it does not mean you must travel at exactly 30mph at all times. 25mph is not THAT far under 30mph to be causing a huge issue to anyone.
People who overtake unsafely as they can't stand waiting just a little bit longer are every bit as bad as drivers who drive too slowly.
I had a driver over take me on a blind bend whilst driving on a country road yesterday, whilst I was towing a trailer. I was not going fast- quite windy road. I am sure it was a little frustrating. I was, however, going at a sensible speed for the road, road conditions and given the vehicle I was driving.
As it was a blind bend he couldn't see that another car was coming in the opposite direction and he had to slam on the breaks, swerve in front of me. Luckily I was travelling very slowly by this time and managed to stop- however, horse in the back slipped and fell in the trailer. Luckily no harm done to horse, other than a fright which I am now going to have to try and overcome. Could have been so much worse though.
Driver on the other hand almost ended up in the ditch. Not that he stopped, of course. Other driver did. I have dash cam and have reported to police. I understand from them that given the evidence they are looking into pressing charges.