I think there is some HP gains by straightening the lifter holes. As I mentioned in another thread when I put my mule motor on my friends spintron, I was shocked by all the movement in the valve train. The end rocker wobbled and their was almost a 2% deflection. Thats why I built a girdle for the rockers, basically the bottom half of my valve cover. For all out racing applications valve terrain stability among other things is key.