Update: After a week with this router in service I have only noticed one problem: If you do not use a fixed I.P. (reserved) for all Xboxes, UPnP can become confused, resulting in strange lag/disconnects from Xbox Live. I'm guessing this has to do with the two units exchanging IP addresses in the midst of the connection, but I haven't tested this theory out by reserving only one of the two. Confusion is evident by single "m" entries occurring in the log periodically (no explanation, just "m": looks like garbage--took only one day to reproduce this). Reserved I.P's have not exhibited the problem, so that's a feasible workaround, and fairly painless. Thinking back, I had to do this on my DGL-4500, so this is probably nothing new, just an old lurking bug.
This is the only thing I've noticed so far, so router gets an A- because of it (stability issue, but easy to workaround, no sacrifice in performance)