Use PBE v1.6. It has a 'one click timing patch' feature that will apply the correct bundled performance timings based on your memory type.

https://bitcointalk.org/index.php?topic=1433925.msg21518785#msg21518785

Just apply the timings, save the Bios and flash it with Atiwinflash. Also back up your original Bios before flashing it.