For those interested, Jeff Volek's team published a study in 2016, "Metabolic characteristics of keto-adapted ultra-endurance runners" [1] that compared fax oxidation. One of the "fat adapted" participants Zach Kibbter, an ultra-marathon record holder, posted a personal writeup that included a table of his fat usage at various VO2 Maxes (a ridiculous 98% fat usage at 75% VO2max and 76% even at 84% of VO2max!)[2]
I don't know the numbers for the general population, but Fig2 [1] illustrates the difference between the high-carb and low-carb arms between the elite athletes, and Fig3 [2] shows the difference in absolute fax oxidation rates between the groups. If you're interested in finding out more, I'd also recommend doing a literature search for "maximal fat oxidation" (MFO, FATmax) - eg, here's a recent (2018) review w/ Fig1 that shows MFO peaking at 0.72g/min [3] (the FASTER trial cohorts avgd 0.67g/min for the HC arm, and 1.54g/min for the LC arm)
If you're interested in some of the other physiological impacts of keto adaptation, here's a presentation Volek gave a couple years ago that helps contextualize both the FASTER trial and a related TANK trial his team ran, as well as some other interesting related performance research: https://www.youtube.com/watch?v=BeS_dhM8dsY
[1] https://www.sciencedirect.com/science/article/pii/S002604951...
[2] https://web.archive.org/web/20201111190720/https://zachbitte...