On August 2, 1998, at 1414 eastern daylight time, a Piper PA-28RT-201, N305RC, was substantially damage after an aborted takeoff and subsequent collision with trees at the Hackettstown Airport, Hackettstown, New Jersey. The certificated private pilot and a passenger received minor injuries. In addition, two passengers sustained serious injuries. Visual meteorological conditions prevailed for the personal flight that was destined for Monticello, New York. No flight plan had been filed for the flight conducted under 14 CFR Part 91. The pilot stated that during the engine run-up at Lincoln Park, New Jersey, the left magneto dropped 70 RPM and the right magneto dropped 50 RPM. After completing the engine run-up, the pilot departed Lincoln Park for Hackettstown, about 1300, with a passenger. According to the pilot, the flight to Hackettstown was normal and he observed no problems with the engine. According to the pilot, after picking up two additional passengers at Hackettstown, he estimated his takeoff weight to be 2,710 lbs. The pilot then configured the airplane with 10 degree of flaps and taxied the airplane onto the displaced threshold for Runway 23. He cycled the propeller once and scanned the engine instruments for proper indications. The pilot then released the brakes at 1,500 to 1,700 RPM. At that point, according to the pilot, everything seemed to be "normal". The pilot then rotated the airplane approximately 1/3 to 1/2 the way down the 2,200 foot runway at 61 to 62 knots of indicated airspeed (IAS). The pilot stated that when the airplane was approximately 30 feet above the ground, he felt it was not performing as expected and would not clear the trees on the departure end of the runway. The stall horn sounded and he elected to abort the takeoff. The pilot stated that the airplane touched-down left of the runway and entered a line of trees. The right wing was sheared off and the airplane came to rest between two trees, requiring the occupants to be extracted by the local fire department. According to performance charts published by the airplane manufacturer, a ground run of about 1,700 feet was required for a PA-28RT-201 weighing 2,710 pounds, at an elevation of 670 feet above mean sea level, 20 degree Celsius, and configured with 0 degree of flaps. In addition, approximately 2,200 feet was the calculated distance to clear a 50 foot obstacle from the point the pilot released the brakes. The calculations were based on a flat runway, obtaining 2,700 RPM before brake release, and rotating the airplane at approximately 70 knots IAS. According to the airplane manufacture's representative, the manufacture did not publish performance charts for a 10 degree flap takeoff nor did they publish any procedures. In addition, the representative stated that the performance charts for a 0 degree flap departure would be accurate for estimating a 10 degree flap departure. The Safety Board Investigator noted a line of trees about 45 feet tall and approximately 100 feet past the departure end of Runway 23. In addition, the investigator observed that the first half of Runway 23 was sloped up approximately 3 degrees.