A quick note: I believe the speed of the tethered connection is artificially limited by the modem script you're using. If someone could test this theory for me, try the following steps:

• Download the following file: CDMA EV-DO script
• Copy the "CDMA EV-DO" file into /Library/Modem Scripts on your Mac. (You'll be asked for your password.)
• Change the modem script you're using from "au CDMA 1x WIN W01K" to "CDMA EV-DO".
• Try connecting. If you're successful, try running a speed test from someplace like speakeasy.net.

Please post the results here.