The .509 set up right makes good power for what it is. I agree the .528 will slow you down and the .557 may not help you much if any other then it's a solid grind and may rev more. If you take the valve lash out of the .557 you wont have much more lift then the .509 and the advertised duration's are almost the same. I agree as I would look elsewhere like advancing the cam. Good luck , Ron