Cisco Switching/Routing :: Nexus 7009 / Maximum Distance For FCOE?

We are looking to deploy two Nexus 7009 cores at our two datacenters. They are approximately 2 miles apart. We are hoping to have 10G Dark Fiber between the buildings and therefore dedicate a pair for FCOE between the cores using 10G Long Range SFP's. I read that the Nexus 5000 series had a limit of ~3 km for FCOE. Does the same hold true for the 7000 series? I thought I read somehwere that the buffers were larger on the 7000 series and therefore would be able to do ~30 km.