The biggest problem with "HIGH" {and as Geistware said this is a relative term} loading is the increase in stall speed. Along with obviously increasing the landing speed, it will slow the rate that the aircraft will transition from level to vertical, instead of a sharp pull up it will sort of mush through the transition. Roll, yaw and the rate of pitch change will not be affected only the path the plane takes through the pitch will suffer. This deviation from the flight path may be so small it can't be seen unless the planes are flying side by side. Geistware, if you really want to see the differance find someone with equal talent to yours and go have a dog fight with the two planes you'll see the change. Also lighter is better but too light a wing loading is bad for 3-D because of its reluctiance to enter a tumble