I would suggest that you just keep doing what you have been with experimenting with different positions ... you just have to find what works for you.
Everyone holds their needles a little bit differently. For example, both my mother and I knit English but I tend to hold my right hand needle very loosely with my right hand on top of the needle (not really sure how to describe it
) while my mother supports the right needle from the bottom, resting it in the "groove" between her right thumb and forefinger.
It just depends on what is comfortable for you. Also, keep in mind that while you knit the fastest with your current method (because that's what you're used to), as you practice with a new position you will get faster as you become more comfortable with it. I would suggest perhaps focusing on finding a position that is comfortable for you and allows you to knit without pain ... speed will come with time!