Amazon.com: AMD Radeon R9 280X 3GB HDMI PCI Express Video Graphics Card for Apple Mac Pro, outperforms ATI Sapphire Radeon HD 2600, 4870, 5770, 7950, 9000, 9800 Gigabyte : Electronics
Refurbished: SAPPHIRE Vapor-X Radeon R9 280X DirectX 12 100363VX-3L 3GB 384-Bit GDDR5 PCI Express 3.0 CrossFireX Support TRI-X WITH BOOST (UEFI) Video Card - Certified Refurbished - Newegg.com
Amazon.com: AMD Radeon R9 280X 3GB HDMI PCI Express Video Graphics Card for Apple Mac Pro, outperforms ATI Sapphire Radeon HD 2600, 4870, 5770, 7950, 9000, 9800 Gigabyte : Electronics
DX12 Video Card List + DX11 Video Card List | Solidly Stated