That's where 1 on 1 lessons come in....
I learned that you don't strike the string when you are speed strumming. You just brush the pick at an angle. It worked like a charm..that's what you get with 1 on 1.
Many years ago, a friend set me up with guitar lessons from David Schenkel, the guitar player of Manowar. I was pretty excited to take the first few before I realized aside from technique he didnt know a hell of a lot about music theory.
Turns out his dad(that he lived with) was the musical brains of the family. Wound up taking lessons from him.
David really added a lot to my speed though. just a few lessons and it went through the roof.
It was pretty sobering to see that whole situation. A semi-famous band, yet the guy had to live with his parents and work at Jel Sert when he wasnt touring.
Great guy, nice as hell, and for all I know he may have parlayed his experience in to a really good life.