Mike, Im just curious, but when did your motor over rev with a 14x4w on it? Mine turns a 14x4w around 11k which for a YS is no where near over revving. As a matter of fact Im considering trying a 13x4w just to compare.

And my YS pulls the 5lb 9oz Flip very nicely. Its holding me vertical at half throttle and pulls out of a hover very nice. But I definately think 6.5lbs would be too much for unlimited vertical..........or decent vertical.