Varies...
The snowblower would operate best in heavy wet snow at the 540RPM mark; keeps it cleaned out and moves the snow farther out of the way. If it is a light dusty snow, running that high creates a cloud that makes a mess.
The backhoe would depend on if it is self contained, or if it operates from the tractor hydraulics. If it is self contained some require 540 to keep the system cool, some you adjust for how fast you want the hoe to operate. With one that operates off the tractor hydraulics, you generally vary the RPMs for the best balance of speed and power you need according to the task.
Best option on all counts is to locate and read all operator manuals for the respective hardware. You could also include the models of the machines you have here and perhaps someone with the same unit could provide more specific information.