To answer Steve's question, slowing the engine speed will slow down the hydraulic flow (GPM, which determines cylinder speed), but it will NOT affect the ultimate pressure, PSI, which determines cylinder force. The relief on most systems is on the directional control valve, just to the left of where the handle attaches to the spool end. Remove the cap nut, and back out the screw to decrease the pressure setting. The relief allows the oil to bypass directly from the inlet to the return core when the oil pressure is strong enough to overcome the spring compression. Lower spring compression = lower bypass pressure. If there is an adjustment on your pump, it is the bypass pressure for the low pressure (high speed) pump. There is not likely a high pressure relief on the pump. If you want to install a pressure gauge, it should go next to the valve inlet, in the line coming from the pump.
As for higher pressure components, I've seen some splitters with advertised capacities dependent on pressures as high as 3500 PSI. While some pumps may be optimistically rated that high, I don't think any of the other system components are rated over 3000, and very likely at least some parts less than that. System pressure should never be rated higher than the lowest capacity component.
But if you're selling splitters, and you figure your customers are making their buying decision based on tonnage claims, you might choose to ignore that last part...
Don