I think it's actually a mix of the game servers, and routing issues to at&t.
You'll probably find it worse at 6 pm than 9 pm, which suggests more US peak time problems than NZ problem...
It was even worse when the outgoing route was going over cogent... so it's curious you're still having such significant issues. It may be that you've got some level of packet loss normally.
Those high pings to the first hop are confusing, but normal. I've seen them be 8 seconds plus...
Its hard to believe it is the game servers, at 10pm last night there was still significant lag, and as I said friends of mine were having no in-game issues - they are on Telecom though. Last time when this was happening, a friend on Orcon I spoke to didn't have any slowness and he is a big downloader.
I'm not an expert, but the sudden slowness I'm experiencing (over the last five nights), and the previous time this happened make me really think it is an issue on the NZ side.
I never thought I would say this but if my friends at Telecom aren't having issues then I may as well change to them.