So for starters, I'm probably the calmest person I know, and that includes on the road. I don't road rage, but there is a strong feeling of bewilderment.
Fair enough if you don't feel comfortable going the speed limit when the conditions aren't ideal (road, weather etc). It's quite often ridiculously foggy round here on my commute and we all crawl through the 50 zones at 25-30, and that's cool, I'm okay with that. Another example would be a stretch of road which is a 40, but it's crazy tight and there's some really sharp corners. Again, I wouldn't really mind if you drop down to 10 through there.
However, when it's dry, clear, and a straight, wide road with no traffic, you have no real excuse for feeling uncomfortable going the speed limit. Even the really slow people manage 50 on the motorway, and that's usually in narrower lanes than A roads and there's traffic moving about all around you.
Also wish people would learn how the different speed cameras work. If it's one of these:
Then you only need to worry about them if they are facing you, and even then, only when you get to the 3 black lines in the road right in front of them.