Chris
Running a lower than specified speeds can do a lot of damage to the hydraulic system
In all of the log splitters I have seen the hydraulic pump is just barely big enough to run the press
Running at less than full speed damages the pump and the valves because the pump will either be running under pressure or at a lower oil flow rate.
If it is a hydro style pump, same as on a mower, and a lot are because they are a lot cheaper than a gear or vane pump the you do a lot of damage to the pump.