Carbonfibreboy.....as you know there is a temperature and power output dependency as to how much one can consume. Although some studies say more than 70% VO2 max causes digestion problems, there is no real formula but I guess we all have to learn our tolerances and I am on the conservative side of eating and not riding too hard. I am going to test this limits Saturday, I'll let you know if I puke. Nausea and diarrhea are reported by up to 50% of marathoners and on a 400k recently I was stunned that a 10,000 KM per year Randonneur who does many 1200k Randonnees said to me that he throws up on all Brevets of 400k and more. Another rider said he often throws up. Never happened to me. I suppose learning our respective limits are worth seeking especially since GI issues are a significant cause of quitting a ride. It sounds you are also moderate in your consumption of liquids and fuels on the bike. The controls on Saturday's 400k are not the typical Mini Marts. Two times at a Biker Cafe/Bar/Restaurant that has great burgers and meals but it probably will be closed when I am going thru, a Pizzeria at 200K, and then at around 360K control, a Mini market. I'm an old school Randonneur and thus, multiple long meal stops are not in my plans. I'll just carry stuff to eat this time.
On a 200k ride recently some of the riders were eating hotdogs (plural) and apple pie with ice cream with coke chasers. Throwing 2500 kCal down the hatch all at once does not work for me. The thought makes me gag.
Over-hydration can be a problem leading to hyponatremia and can cause GI issues and more serious medcial concerns (outlined in some of the links)
Reasearch suggests that endurance athletes should drink when thirsty and nibble all day long and also lower intake before big climbs and/or ride easier during the hot part of the day. Drinking when not thirsty to excess is easy to do and it can make you puffy all over and the risk is not just a temporary weight gain during a long Brevet.
Anyway, I hope this helps someone on a long hot summer ride.....
Food-dependent, exercise-induced gastrointestinal distress
Gastrointestinal Complaints During Exercise: Prevalence, Etiology, and Nutritional Recommendations
Over-hydration - Too much of a good thing? Succeed! Sports Nutrition
GASTROINTESTINAL DISTRESS
Exercise-Associated Hyponatremia
Waterlogged: Seven clear symptoms of Exercise-Associated Hyponatremia
Sounds like you have a good handle on it. As they say at Hammer, "Less is more." I've never thrown up or eaten a "meal" on a long distance ride. How funny, the only mini-mart at 360k. And how tough for the participants and the cafes, to have to get cards signed and water and restrooms without buying anything. That's usually a no-no.
If you do overeat a bit, I call it "sloshy belly." That's what it feels like. That's very common and really bad because you can start to bonk simply because your stomach osmolality is too high and nothing's going across the stomach wall. The cure is to stop eating, take 2 Endurolytes, and then sips of plain water every few minutes until you get relief. That's why it's so important to have plain water aboard and to only eat a little at a time.
A local maxim is "there is no slower speed than stopped." Best to keep control times short and keep rolling.