FEL = all tractors should be able to use both curl / lift at same time. a HIGHER RPM = more GPM (gallons per minute) and will cause things to move quicker. you are getting the same PSI (pressure) going to both curl/lift. it is just dependent on GPM (gallons per minute) the other factor is diameter of the hyd cylinders.
as others have said "skill" can be a big one.
FEL (Control valves) can differ alot. some real cheap basic control valves, and then some valve setups that offer say regenative. hyd oil goes to lift, then from lift to curl, and then curl back to valve. (everything is in series kinda vs parrallel), there is also quick dump (i forget correct term) but allows loader to "power down or fall down much faster"
some FEL's have kinda of an auto leveler, more so for general duty buckets full of say dirt / rock. and keeping the bucket in correct position so crud does not roll back down onto tractor when lifting the FEL.
some FEL's control valve setups have a "float" you adjust the curl of bucket and then arms of the FEL go up and down freely as you go over the ground. much like a 3pt hitch.
most of the bigger manufactures have a "custom build tractor" pages, and have a page if not a few pages of "additional options" many of these extra options can be extremely handy. go through each "additional option" and then google search it / youtube search it.
Tractor Attachments And Skid Steer Attachments For Any Tractor Or Skid Steer has some nice video's showing / explaining a lot of difference pieces of equipment.
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about only thing additional i can think right off the bat is "third function valve / joystick" for a FEL so you could run say a grapple on the FEL.