Hi Tim,
Interesting osbervation. In the past if you mix and match Frimware NDIS and ACU versions then you will get different receiver sensitivity "reported" results.
Can you post or email me (derwin@cisco.com) a table showing
for each card ACU version NDIS version and Firmware version and the approx age of the card or serrial number if you wish. and signal strength recieved
Also are you using the same laptop and AP for all cards during the test