How much extra lift are you going to get (with an extra 100-200psi) and do you really need it. Going up from 900-950 (stock) to 1350 seems reasonable. I believe I will need about 1.2mm to do that (4 x 0.3mm). That is about a 50% increase in pressure, but likely less than that in lift capacity. The extra 10% doesn't seem worth it to me. Going even higher seems like much more likely to cause an issue, eventually.
It takes a certain amount of pressure to raise the bucket. Anything above that pressure is applied directly to payload capacity, less the effects of geometry and leverage, of course. Adding 50% to the relief pressure will possibly add more than 50% to the lift capacity. If you have to ask if the extra lifting capacity is really needed, it's because you've never pulled fence posts with a ball of concrete on the end. Believe me, it's needed, along with a couple of other tricks to further increase payload capability without adding strain to the pump.
SCUT loaders use the same size cylinders but with a 2000 psi relief valve. If the arms of the GT loader are the same length as the arms of a SCUT loader, the lift capability of the GT at 1500 psi (max) will be something considerably less than the lift capability of the SCUT. Most SCUT loaders can barely lift 1100 lb off of the ground to transport height.
This is an excellent thread for ballasting a loader. Weights were measured at a truck weigh scale and are tabulated in Post #10.
Note that many of the older GT loaders used 2" diameter cylinders rather than the 1.5" diameter cylinders on more recently made loaders. A 1500 psi relief setting will easily lift the rear wheels off of the ground with a ballast load of 650 lb. Payload capability for those GT loaders with that high of a relief setting is well over 1250 lb. It just takes more ballast to be able to transport it.
