Bus, I've never tried for a negative split, any more than I've nominated a race to try for a pb. Both concepts are flawed. It's cart before the horse thinking.
It's the same with in race 'number forcing', where the runner wastes energy fretting about hitting targets and worrying when they miss them. Again, it's thinking about the wrong things.
It's decent training first. Because that's the easiest way to run well. Then in a race, it's concentrating on effort, style, efficiency, breathing patterns, all things in the 'now' which can be controlled.
Luck, shipping extra pain and a following wind seems to be many runners idea of how to get a pb.
I want to run easier and faster. That's why I've gone on a diet - it's speed for no effort.
CC, I should have added that there's the first rush which wipes out a load from around 400m.
Most are simply running as fast as they can go at any moment in time. The reason they come back at around ten minutes is their blood lactate levels have hit maximal levels.
That's why I catch so many and pass them after that time.
If a road racer wants to hit optimum average pace for the entire race, they have to set off at what feels like 3/4 pace, and be prepared to let all and sundry go ahead of them, sometimes almost out of sight.
That takes confidence and nerve.
I don't do 'banking time', because it yields an inferior result to correct pacing. It's physiologically speaking, inefficient.