Personally I have experienced that 8-15 reps are best for packing on muscles. Sometimes I go as low as 4-6 reps in squats, bench and deadlifts just to get some extra poundage on the bar.
Another thing witch many people forget is variation. If you have trained with 8-12 reps for a long time, you may grow even more by using the 2-6 rep scheme.
And OTIS, you can not change the genetic shape of the muscle no matter what..