range for Cisco 7920 VOIP

I am attempting to find some specifics for what I could expect for a
coverage area for a wi-fi Avvid phone.

Cisco does suggest that the unit is not ruggedized and therefore, not
appropriate for outdoor use. So assuming I have the sense not to talk in a
typhoon, I want to figure out the prospect for using 7920's outsdoors in a
small MAN (<1 square mile) with unidirectional antenna coverage. Can anyone
help me translate what the 90dBm means in terms of range

The info I found from Cisco FAQ:
Q. What are the requirements for signal strength and quality (from the
access point) for optimum voice quality on the Cisco 7920?
A. Cisco recommends that the relative signal strength (RSSI) be equal to
or higher than 20, which is around -90 dBm. Also Channel Utilization (CU)
should not be higher than 45 (requires QoS Basis Service Set (QBSS) to be
enabled on the access point).

I have asked 2 CCIE's and they feel it would be a matter of experimentation.
I'm hoping to come away with a good/bad feeling.

Thanks,
Todd

I went out and found a clue:
Orinoco silver card:
11Mbps -82dBm
5.5 -87
2.0 -91
1.0 -94

I assume that to mean, all things being equal, if I can get ~2.0Mbps or
greater with my PC card, I would have success with the 7920?

Thanks,
Todd