Out of interest how can you be so sure that the CPU is not throttling the game?
If you have a ASUS mother board simply use the automatic level up feature or overclock your CPU to just over 4GHz and see if there is any improvements. If yes the throttling is happening, if no then definitively there is not. And we can proceed with trying to find a solution that does not require AMD to provide a fix if possible.
To help us help you - please provide as much information about your system and the problem as possible.