The easiest way to test your new setup is to saturate the upstream with low-priority traffic. This depends how you have your priorities set up. For the sake of example, let's say you've placed telnet traffic and ping traffic at a higher priority (lower fwmark) than other high ports (that are used for FTP transfers, etc). If you initiate an FTP upload to saturate upstream bandwidth, you should only notice your ping times to the gateway (on the other side of the DSL line) increasing by a small amount compared to what it would increase to with no priority queuing. Ping times under 100ms are typical depending on how you've got things set up. Ping times greater than one or two seconds probably mean that things aren't working right.