The pilot reported that he was attempting to land on a 2,800-foot long turf runway. He planned a landing to the north due to obstacles along a southerly direction of landing. The pilot added that he approached with an approximate 5-knot tailwind and the wind was not a factor. He further stated that on final approach, the airplane was a little high. During the flare, the airplane floated longer than the pilot expected. At that time, he did not want to perform a go-around due to power lines at the departure end of the runway. The airplane subsequently touched down about halfway down the runway and the pilot thought that he had adequate distance to stop; however, the grass was wet and down-sloping. The airplane traveled off the end of the runway and the pilot veered left in an attempt to avoid power line poles, but the right wing struck a pole and the airplane came to rest upright. The pilot further stated that there were no preimpact mechanical malfunctions with the airplane and he would have performed a go-around sooner, if he knew the grass was wet and down-sloping. Examination of the airplane by a Federal Aviation Administration inspector revealed substantial damage to the right wing.