Dicky is struggling to his notion that there is some point point beyond which pushing incurs a risk far greater than the reward. This seems to be a revelation gained from inspiration from Craign Gordon's incredible ride at 24 hour worlds in October in which he dethroned Chris Eatough, prevouis world champ 6 years running. For his extreme efforts, he was rewarded with kidney failure, a 3 day stay in a hospital on a dialysis machine and who knows what other maladies.
Here's another take. We don't know exactly why Gordon suffered the problems he did...but it has to begin with dehydration and/or improper nutrition during the event. Yes, he was tearing down muscle for fuel and that's what gummed up his kidneys...but why did this happen in the first place? It's no wonder he didn't have all the nutritional details of a serious 24 hour bid nailed down tight - it was only his second 24!
The way I see it, PB performances come as a result of impecabble preparation and smart execution. You toe the line relaxed, confident in the work you've done to get there. External stresses are non-existant, you are focused in the moment. As the event unfolds, it is effortless, not difficult. Your mind is clear, you stay on task, fueling & hydrating wisely, staying within the bounds of your pacing plan. Even though it is effortless, you are hauling ass.
Of course, there comes a point when it isn't so effortless. But, provided you really are ready for the event and stay on top of fueling and hydration (and this is your top priority event), as the level of effort required increases, there is no point beyond which you should not push. You are prepared for the effort, both physically and mentally, and that's why you are there.
Just give'r.