The pilot of the Cessna 172N departed on a cross-country flight; however, shortly after takeoff, he became concerned because the engine tachometer showed 2,400 rpm, when he expected to see 2,600 rpm. The pilot elected to return to the departure airport to make a precautionary landing. He subsequently performed three missed-approaches to the 2,500-foot-long, asphalt runway, due to high approach speeds. On the fourth landing attempt, the airplane again approached at a high approach speed, and the pilot attempted to bleed-off airspeed during the flare. The airplane touched down at a higher rate of speed than normal, bounced, and then settled on the runway. The pilot was not able to stop the airplane before it departed the end of the runway, and impacted a fence. Examination of the airplane by a Federal Aviation Administration inspector did not reveal any preimpact malfunctions. At the time of the takeoff, the pilot was not aware that the airplane was equipped with a "cruise-propeller." Winds reported at an airport located about 5 miles northeast of the accident, about the time of the accident, were variable at 4 knots.