It is totaly wrong to think that the handicap is coming from the lack of the push-offs from the wall. This has very very little effect if any. I can speak for myself but I had one or two experiences where I had to swim DNF in 50 meter pool and the problem for me was a sudden loss of orientation in terms of the distance to the wall and overall distance. As a result I lost my calm and had problems to find motivation. So to speak about 0-10% loss is really risky. I think it can lead even to abandoning the dive. But of course some can swim even greater distances and make their PB's.