I forget what I have written on my experience with ketosis but wanted to correct a few erroneous comments by others. Bonking is when the brain lacks sufficient energy substates and you just doing into ******g la la land. Glucose, lactate, and "ketones" can all burn just fine upstairs. Some equate bonking with depletion of glycogen in the working muscles but that really is not bonking; nonetheless, a properly fat adapted keto endurance athlete cannot bonk. Period. I have ridden very long distances at reasonable efforts (around 55-60% of VO2 max) with no food and did not bonk. In fact, I would characterize myself as having been bonk-proof.
WRT to long endurance riding, the limits are not power. Rather, they are primarily energy source limits and fatigue. A high ability to burn fat is not the exclusive domain of keto athletes.
Having been a keto athlete, I would never have denied my ability to call on glycolysis when needed despite the fact most of my event depended on my ability to utilize lipolysis. Practically, it just meant I needed to eat fewer carbs to fuel the ride. The benefit to lots of miles or volume just around the LT1 threshold is developing lets call it the mitochondrial engine (without getting into enzymes, transporters, and signaling). Type 2 and type 1 muscles are always being used. When below LT1, almost all of the lactate is being used for fuel and is not being seen when you stick your finger or ear and measure lactate. That is the reason world class swimmers, runners, and professional cyclists do tons of volume. One could think of the type 1 fibers as gigantic vacuum cleaners for lactate or alternatively, the glycolysis provides the energy for the type 1 fibers. How does an endurance athlete get to a fractional utilization of 90-95%? Not on Trainerroad.
Fat people have such messed up metabolics that it (hardcore keto) really does not apply to most of us although I can appreciate the benefits. I could eat as little as 30g of carb on a rest day or as much as 300g on a ride and still be in ketosis.
I went out of ketosis on the Trans Am Bike Race (TABR) because it was impossible to do on 4300 mile self supported race. Was I slow as a keto athlete? My key brevets were all done in less than 60% of the allowed time and I was working on doing them in under 50% of the allowed time. I did PBP in 54 hours solo. I ain't never seen no club rider do that no matter what they did eat. So, Keto can work. I don't do it no more. It is a lot of work when you are married to an Italian wife who loves pasta and pizza. I plan to do my brevets in 2023 and PBP out of ketosis but I am older and better, so, I expect to get faster.