Hi,
All devices on the SSID are the same and support 11g, I suppose it's possible another device on another SSID could be limited to 11b on the same AP. I'll see if I can find a scenario where only this SSID exists so I know no other devices will be associated.
Under what circumstances would an 11b client in the area cause the slowdown? You mention the same channel, is that including unrelated APs, I assumed it would only be clients on the same Radio? Is there an Aruba document or ortherwise that can explain it that you could link me to?