I have known George for several years now, and own 3 sets of his dies. I have come to expect nothing but the absolute best from him. His knowledge and products are top notch.
There are a number of reasons that bullet material is more important than concentricity. While concentricity is important, material is more important. Gilding material is supposed to be 5% zinc and 95% copper. This amount of zinc still allows the copper to be soft enough to form well, and engrave well by the lands, without excessive metal fouling. If the jacket material is too hard, your bullets won't be as round due to a greater amount of spring back, won't form as smoothly, have a greater chance of folding a point, will have greater variation overall in the scrunched nose area, and have a greater tendency to foul the barrel. Others may be able to tell you more negative side effects, such as poorer grain structure viewed under a microscope.
While concentricity effects the balance of the bullet. You have to keep in mind the .001" jacket run out, while sounding horrible, only moves the lead core off center by .0005". The actual unbalance is far less, because it is the difference in the weight of the copper and the lead. Another words, where there is less lead, there is more copper to offset the weight of the lead, and vise versa. Keep in mind that the weight of lead is .39 pounds per cubic inch, and copper is .31 pounds per cubic inch. That is only .08 pounds per cubic inch difference between the two materials. That is why better material makes a better bullet. Also keep in mind that a softer jacket material will draw a more concentric jacket, so that is why George says it's all about the material.
I have made my first batch of bullets on the new Sta-Moly jackets. There is no doubt that the jackets are softer and point up nicer than the J4's. Haven't shot any yet, but was extremely pleased by the way they formed. Since they were 30 caliber, I'm sure the softer jackets were even more noticeable than a 6mm. I would guess around 25% less effort on the handle. The early performance of the Sta-Moly jackets has come from great attention to the material consistency, and concentricity.
Michael