Here is the classic distortion. It is based on the Proco Rat and it is mean. I find it to be very trebly and have to really turn down the treble to keep it usable. I also have the gain at like 45% so it can be much nastier. It is a good chunky rock pedal though. Winner in my book!
http://www.head-fi.org/t/614949/audio-technica-m50-vs-shure-srh-840-vs
http://www.head-fi.org/t/615411/shure-srh840-vs-audio-technica-ath-m50