Mreeb:
12.8 gpm @2,000rpm, even at only 2,000 psi, is 15-18 horsepower (depending on pump efficiency, line size, etc.) Unless you load a log splitter much faster than I do, that should be more than adequate for a 4" or even 5" diameter cylinder. It is certainly more than enough flow for a FEL. For example, the FEL on my Kubota Grand L4330 lifts 2500#+ faster than I usually want it to on 9gpm. My John Deere 455D crawler loader lifts 10,000# faster than I want it to on about 20gpm.
Unless the new pump is very cheap and easy to install, I would try the old pump first. You may discover something else to spend the money for.
But if you do get the larger pump it will increase the heat generated when the fluid is just circulating (by 50% unless the lines are so small that the flow becomes turbulent when it increases), but that heat is usually insignificant. You will also increase by 50% the heat when the system is working hard, and that might be a problem, if the system heat dissipation capacity is matched to the present flow. But you can easliy measure that with a hand held thermometer on the fitting nearest the pump output.