As an aside, TAC was able to steer me to a more generic doc regarding trimming rates. It had some findings in there about Xbox and Wii that I think is worth noting.
I tested the g-basic and g-beacon rates, per their recommendations and it works fine btw.
We will test the Wii tomorrow but the Xbox supported these rates:
wlan ssid-profile "ssid-XXXXX-Wii-TrimmedRates"
essid "XXXXXX"
a-basic-rates 12
a-tx-rates 12 18 24 36 48 54
g-basic-rates 5 11
g-tx-rates 11 12 18 24 36 48 54
max-clients 255
wmm
wmm-vo-dscp "56"
wmm-vi-dscp "40"
wmm-be-dscp "24"
wmm-bk-dscp "8"
mcast-rate-opt
g-beacon-rate 5
a-beacon-rate 12