Join Date: Dec 2000
Location: Cincinnati, OH USA
One quick thought... most of the pedals mentioned here (such as the TS9, and the way most people use the DS1) when used in front of a tube amp don't really give you a new distortion sound, but generally the same distortion sound your amp has with a lot more gain. Petrucci's sound is pure Mesa, so I don't know how satisfied you'll be putting any overdrive-type pedals in front of a Marshall.
If you really want Petrucci's tone (and don't want to trade the Marshall in on a Mesa), consider looking at some of the Mesa tube preamp pedals. They'll be a little more expensive, but they're built like tanks, and are likely to get you closer to the tone you're looking for. The Bottle Rocket is a single channel preamp, and the V-Twin is a two-channel preamp. I've owned both, and I think they have great tone for the money.