Fully upgrade everything. Go off the ramp normally at 6% resistance. Glide for a few seconds to gain altitude, then drop to 3% or 4% resistance. Then, use your rockets in small bursts to stay in the 130-150 mph range. You will continue to drop, but will be over 110 mph when your fuel is gone. Continue gliding, and when you begin losing height, drop resistance to 0% to build up speed and get a good bounce off the water. Bounce, wait a moment, then drop resistance back to 0% again. You should get 6,000 feet before hitting the water a second time, bounce a second time to reach that height.