larrybf: Good question. So far, looks like you need to do pretty high volume to get better rates.
Looks like range of $6-8/RT is current low, and that a $1-2 difference in rates would be overwhelmed by other factors such as timely quotes and faster executions, since, for example, picking up a single $10 NQ tick or two will pay for a $1-2 rate difference if making 10-20 RTs/day. Anyway, the fixed cost (spread and commissions) of trading 1 NQ contract at these rates is already about half that of trading the equivalent 800 shares of QQQ (even at IB's low rates), which is a big improvement.
If, however, someone out there knows of a better deal as of 11/16/2001, please speak up!