I am planning on upgrading my PC so i selected the required components
Processor:AMD FX 8350
GPU:Sapphire Radeon R9 270 Vapor-X
RAM:Corsair Vengance 16GB 2X8 GB
Hard Disk:WD Black 1 TB
Motherboard:Asus Crosshair Formula V
PCIe is backwards compatible. Your board is PCIe 2.0 and your GPU is PCIe 3.0. Since it is backwards compatible, your PCIe 2.0 motherboard will support a GPU that is PCIe 3.0 but the GPU will basically fallback to PCIe 2.0 mode to maintain compatibility.