Though it's rather peeving when you get people playing 'pace car' in the outside lane, driving at exactly 40mph on their speedo (or sometimes less) with nothing in front of them and plenty of opportunities to move over.
I know about the speedo error on the Lag, and how it relates to the cruise control display and true speed according to GPS. I tend to do 40mph roadworks at 42mph on cruise or limiter, which is about 43-44 on the speedo. In reality, I'm doing 40mph.
But you get these idiots whose mentalty must be "I don't want to get a speeding ticket, but I want a clear run to hoof it once I pass the last SPECS camera. (Besides which, if anyone passes me, my genitals will drop off.)" Halfords should sell rocket propelled grenades so you can blast the muppets off the road
As for the limit, I got away with averaging an indicated 50 over Thelwall's SPECS enforced 40 limit for several years. And before anyone has a go at me for putting the road works crew at risk - they were working on the other bridge!
The real fun of SPECS is watching people slow down for the cameras. Obviously they'll get a better understanding of how the system works once the NIP arrives in the post
And out of interest, plod has recently been siting a camera van on a bridge just past the end of the Weaver navigation works on the M56 heading Westbound. I think the plan is to catch people who hoof it once they've passed the last SPECS camera, even though they're still in the 40 zone. If you're driving on that stretch, then it'd best to observe the speed limit for the full length of the roadworks.