Un-amplified PLC over powerlines with NO pole transformers in the path, maybe 200-300 ft.
RF? maybe 150 feet, no walls.
However using single phase PLC amplifiers like Jeff Volps XTB or Smarthomes Booster Link you might be able to leap frog PLC very long distances, as long as there are no pole transformers to be crossed. If there is 220V ("two phase", "dual phase", "split phase"... pick one) to all bulidings then you would use XTB IIR or ACTS CR234 as amps.
Finally you might also go to Sand Hill Engineering (
http://www.shed.com) and email Michael, posing the question. Mike, a genius from NASA, has a huge ranch in Florida and drives X10 signals everywhere on the ranch. I know he runs several well pumps by X10 which are distant from the office.
"Xtension" is a MAC home automation program from Sand Hill that has been around since the late 1980's and has been able to do things that is still called "State of the Art" by todays automation software publishers. My first talking house in 1994 was using Xtension. Michael was always most helpful.
Mike can probably give you a very accurate answer after 300 milliseconds of deep thought.
