Yes, the motherboards are support Gen3 link, but SB-E C1 stepping is a faulty revision. Intel didn't released the server platforms for this reason. They are waiting for C2 stepping, because the server market is different. They can't say it maybe support PCIe 3.0.
The real problem with C1...
Intel never said that Sandy Bridge-E support PCI Express 3.0. They said maybe support it, or maybe not. The Sandy Bridge-E has a PCI Express 2.0 controller as PCI-SIG officially certified it. On the motherboard side, the Gen3 link is supported, but it need a CPU, with officially certified Gen3...