I learned that the WSM has a "high temperature coating/ paint" on the mid section, the Pro Q doesn't. Pro Q doesn't warranty damage because of high heat to the stacker section. Here's the link http://www.fredsmusicandbbq.com/ProQ...prqexcel20.htm
It's not much of a difference, but it was enough for me to go with the WSM. Also in the Youtube videos mentioned, they test the pre '09 WSM. The '09 WSM has a thermometer in the lid & a much larger water pan (approx. 2 1/2 gallons, my measurement), an exterior heat shield + other minor changes. This is for the 18 1/2 inch WSM not the 22 1/2.
just my 2 cents