The other program I used was AJA KONA SYSTEMS TEST. I mounted a drive from my mini, set the prefs in Kona to allow network drives, then have it generate a 1GB file. Below is a test I just did. 10.4MB/s = 83.2Mb/s, which isn't bad. Almost as fast as wired 100Mbps connection. (But not faster than the 100Mbps ports on the back of the router). 😉
Have you seen the status screen in the AirPort Utility that shows you how fast each of the wireless clients are connected? That's pretty cool.