I don't claim to know a whole lot about the sport, but...I fooled around with platform diving at Texas, and used to cliff jump at Minnewaska, and other quarries in the area. My longest jump was about 80 feet..a true 80 feet,(many times people over estimate diving cliffs).
Three words, don't do it. I racked my back really bad once on a 55 footer.
The guy to chime in on this, I believe is Jon Pandragon. Jon, didn't you used to dive for Florida?