Last I knew, and I'll admit I haven't looked recently, the gigabit was actually limited to something like 480M. The only other one I can think of that is armv7+ (that isnt mx6) with gigabit is the OpenBlocks which has 2 or 4 gigE ports but there is no video on it.

Depends on the packet size. With 64k packets, you can easily approach 800M. But, yes, default packet of 8k will yield 480M at best.

This is the latest update it seems http://boundarydevices.com/i-mx6-ethernet/ but that is decent for a consumer type ARM device (I presume some of the server options do better).