your mobo and cpu support pci e gen 3 ?
i am using an sapphire rx480 4 gb on  pci e gen2 and he got same speed like you because this a nice bottleneck 

hi guys i have a maybe foll question im using an rx480 card with crimson driver everything is rock solid but i want to use the enviroment variables like gpu max alloc percent the new wont allow the old variables and the qustion is i need to find the new enviroment variables or is not needed anymore? sorry for my bad english i wont speak well