Just to be clear, I am not "broadly" advocating the operation of the FEL without rear
ballast. My question, however, is based upon the premise that a safe, unballasted, operational weight does exist. To contend otherwise would be to accuse the manufacturers of purposeful endangerment. If, in fact, safe operation in the absence of additional equipment is impossible, legislation should be imposed to mandate the inclusion of that equipment with the delivery of any FEL.
Having said all of that, I fully agree the weight is subject to a plethora of environmental factors. Further, it may be the weight could be 10lbs, 100lbs or 10000lbs, depending upon the particular tractor and its specific setup.
Perhaps the question should have been posed in a more clinical fashion ... On a solid and level surface, at a speed of 1 mph, with the FEL equipped with pallet forks and being raised 6 inches from the ground, with no wind and a temperature of 72F on a partly cloudy day, what is the maximum safe limit that may be raised with the FEL sans rear ballast? I guarantee you there IS an answer, otherwise a case of gross negligence exists and some manufacturer is eventually going to be massively and successfully sued.
Just my 2 cents and I realize your mileage may vary