While you may not need the RPM's for the power to pop the log, it will be slower at a lower RPM.
1800RPM will only cycle half the speed of 3600RPM.
And it really dont make it much quieter IMO. We have a 3-phase motor on one of the splitters. Its still loud. Hydraulic pump whine. Not as quiet as we were hoping for, but still nice to split indoors where its warm and not fume yourself out.
Fuel consumption is nil. On my 16.5HP/22GPM combo AND on dads 6.5HP/11GPM combo, its maybe a quart or 1/2 gallon per cord. Not enough to even worry about IMO