The simple fact that such a small range of sizes are deemed satisfying is what makes the chart bullshit. It says no matter what, the average man has no chance of satisfying a woman. Having a bigger dick helps out in bed, but if you can't satisfy a girl in bed it's probably because you don't know what you're doing, in which case having a big one is worse than a small one. I remember reading about how they tested dildos, and that was almost definitely biased. I bet they did slow strokes straight into the pussy, and used the same strokes on each dildo. I doubt they took into account the agility of a smaller dick. I remember when I was smaller I could hit girls from all sorts of different angles and pinpoint spots inside them well to get them off. For the larger sizes notice how the perfect length was about 7.75" length. They probably didn't take CDL orgasms into account, and probably just rammed the dildo against the girls cervix.
What I'm saying is that while there are ideals you should strive for, you don't need to be any kind of size to satisfy a girl. I hate to see guys being convinced that they are useless as lovers unless they are 8X6, because it's wrong.