Routers don't really have a range. I'm guessing you have a wireless router, in essence a router with integrated Access Point. The AP will have a range. For accurate signal strength and quality I'd recommend netstumbler, assuming your client card is supported and most are nowadays. For throughput I prefer FTP, however you could also setup a webserver and download files from the client that way. That's a couple of basically free methods that should give you an accurate reading.