Mining Rig 5 GPUs - which Mainboard?

Hi guys, I want to build a mining rig with 5 GPUs, probably all ATI 290x or some 280x. Now the 290x is using a 16x PCIe 2.0. Which mainboard is suitable for this rig, without losing GPU speed through limiting the data transfer? I thought of using one with PCIe 3.0. and 5 16x or can I use something different without losing bandwith? I am not a gamer so my knowledge is limited about this part.