I find BX max pressure is established at <>2000 RPM, increasing RPMs beyond that does not lift more just speeds up actions. I raised my pressure to 2000 PSI so can lift a little more. Never really tested comprehensibly like the OP. I assume everybody knows to get the weight as close to the tractor as you can to maximize weight capability. I can lift a lot more with a chain anchored just under the curl cylinder. I use bucket mounted forks. The FL attachment that replaces the bucket will lift more being closer to tractor.
Ron