Hello everyone,
We just updated the Mantle Known Issue page for the Catalyst 14.2 Beta driver (here is the link: http://support.amd.com/en-us/kb-articles/Pages/Mantle-Known-Issues.aspx).
It now elaborates on the support for the 280X:
"Mantle performance for the AMD Radeon™ HD 7000/HD 8000 Series GPUs and AMD Radeon™ R9 280X and R9 270X GPUs will be optimized for BattleField 4™ in future AMD Catalyst™ releases. These products will see limited gains in BattleField 4™ and AMD is currently investigating optimizations for them."
I get a 404 page not found error from that link btw