If your problem is solved, please consider marking this topic as [Solved]. See How to mark a topic as [Solved] for a short how-to.
(in this case, the problem probably isn't truly solved yet, but by testing the connection to a computer and verifying the same behavior of 100Mbps connections, it seems likely that this is an ISP/cable/termination issue and not a function of OpenWrt... thus probably makes sense to mark this as solved.)