Sorry for dredging this up - is this actually true that the same width tire on a 700 is faster than a 650?
I regularly switch 700 and 650 on my gravel bike with various tire sizes over many years and can’t say I’ve noticed this, though I haven’t tested it. One thing I have found is a 48mm 650 feels way better in handling compared to 48mm in 700. The 700 with a larger tire feels awkward IMO.
The 48mm in 650 is approximately the same diameter as 28mm in 700, so I’m not seeing why the 700 would be faster given the same tire width. Are you aware of a test that shows this?
Also, the ride height with the 650 is lower and may be more aero…