Exactly, nothing to be gained by speed except having to think faster, draw more air in, which laden with carcinogenic diesel fumes and cleaner petrol fumes.
And there my personal suspicion at the rise in lung cancer, it is not the tobacco smokers who are being blamed, but the rise in diesel engined vehicles, because a study was done comparing the 1950s when just about everyone smoked, even in hospitals and the present, when it is considered almost illegal to smoke anywhere, the results were such that in the 1950's there was less lung cancer, but now we have more, so something isn't computing here, but one thing is for sure, nearly every other car is a diesel, whereas in the 1950's, it was commercial vehicles, and not many of them, because petrol was far cheaper. It is simple really, who are governments less inclined to piss off, the tobacco industries, or the petro chemical indusries.
But one thing I do know, diesel contains at least four known carcinogens, and we are breathing it all the time, it is everywhere, just look for that black dust in your house, the dust is there, you are breathing it.
The buses are the dirtiest diesels around, so if you commute, wear a respro mask or similar, as in traffic, I would say one is not getting any healthier, one is getting worse, by breathing in more air than normal, air laden with fumes.
As it is with me, when I cycle into town, less than a mile away as the crow flies, there is water between town and me, so it's six miles around, cut down to four miles due to a cross country route until I hit the Billacombe road and Laira bridge and the traffic disaster there.