Ubuntu 16.04 is not a supported distribution, so our drivers may not work as intended.
Have you added the application to additional settings and set it to run in High Performance mode? If you enable the switchable graphics application monitor, which will tell you which GPU is being used in which application.
Actually whatever performance your getting that is going to be it , if you follow Matt's advice you will see that even if you set an application to High Performance the system will never use the discrete card it will only use the APU or primary card. Cause every application will say Power Saving except those that actually have a working crossfire Profile!