I did say that I'm perfectly happy with my 28s, so I mostly agree with that. But 1.8% difference in total drag is more than I'd previously estimated that difference to be, and if it works out to that I may reassess. I have almost 50% reduction of drag by other means already so it wouldn't make that much difference, but every bit extra speed or reduction of effort is that much more fun.

Unfortunately, I suspect that it doesn't really work out that way since much of the wheel drag is due to the spokes and hub area and it may be that the 10% number includes that also. I've found for example that covering the rear wheel spokes with disks reduces overall drag somewhere around 2-4%. If that is the case the improvement from 28c to 23c tires would be considerably less than 1.8%