Both of these ball types are rated with extra distance and also with extra spin. It is true, you get more distance and you get more spin. However, you do not get both in conjunction with each other. The bug is in how the ball distance modifier is being treated when backspin is applied. The variance between using backspin on a shot with these balls as compared to not using backspin is extreme.
For instance, using my Ping G10 Master 5 iron, rated 175 yds, and using an SD ball, I can get a result of about 178-180 yds on level ground using neutral spin. However, if I apply full backspin to the shot, my ball will not only carry less distance in the air (a clear anomaly considering every other ball has its carry distance increased with backspin), but it will only fly average between 170-172 yds. If I was getting the benefit of both the extra distance modifier and the extra spin modifier, my ball would carry in the air further and stop faster, not carry less distance, In no way should a ball with 2 dots of extra distance end up with less distance than the club rating when backspin is applied, yet this is the case time and time again.
If I had to venture a guess, the distance modifier is being negated when the backspin on these balls is being applied. We are ending up with clubs that can have up to 10 yards worth of distance variance, and this is not factoring in any of the normal deviation or "beast". This is not how the balls should affect a shot.
If I use that same 5 iron and hit it full power with an SD ball, it should go 178-180 yds. If I use full backspin I would expect a result of 175-178 yds. As I said above, in no way should the shot ever go less than the rated distance with a ball that has an extra distance modifier. Please adjust the calculation for how the backspin modifier affects the distance.