I don’t think you really get places that much quicker by overtaking. A few minutes at best, no matter what car you drive. If it’s someone cruising along at 40 I don’t bother anymore, the number of times in my youth I would get past someone like that, then when I’d arrived or stopped much further up the road, see them come cruising past me like 5 minutes later. These days, I see folk getting past me, and then I see them stopped off somehwhere much further up the road, looking like they more or less just got there. I think it’s because the 40mph cruiser doesn’t really brake or accelerate, whereas someone wanting to do 60 or more has to brake and accelerate loads, wait behind the next 40mph cruiser, get past them and so on, so the avarage speed isn’t that much higher than 40 for anyone no matter how you drive. Best just to save fuel, tyres and brake pad material and chill I reckon, do 60 if you can, but if you’re stuck in a line at 40, just roll with it, it won’t really make any difference. Safer for all that way too.
60 is a limit, not a target.