The longer brace height being more forgiving is a myth. I haven't seen it make any difference.
I have a bow I'm comfortable with that is 7-inch brace height.Dont worry about the speed thing. Get a bow you are very comfortable with, keep it tuned and shoot a COC head. You will be just fine. I also find that you can shoot higher poundage on a more forgiving bow compared to a short brace height aggressive cam bow as well which makes up some of the speed difference.
Some advice here, don't ever try a 6" BH you might wind up buying it LOL.