for the speed boost you should use kernel x11/x13mod and clean install new drivers v14.6/rc2, like this: https://bitcointalk.org/index.php?topic=623409.msg7642920#msg7642920

for to fix the HW at amd v14.6/rc2 errors follow this post: https://bitcointalk.org/index.php?topic=658438.msg7555998#msg7555998