For the last 6 - 8 weeks i have found that a 3/4 back spin on any club i have gives the most back spin distance. A 3/4 top spin against the wind seems most effective also.
I think that a full back spin takes away from the launching of the ball and ultimately shortens the shot. The full front spin causes the ball trajectory to be to shallow and it hits the ground to soon.
Try the 3/4 setting. I did, and like it. My nickle.
ps, I always use backspin against any direction on side winds, will give you extra yards.