Re: MXR Classic OD internal switch
On it's own the ZW is weaker and more midrangey, people say it's flat, but it's not. It works real well to tighten up a secondary gain source after it, in my case the MarkIII or a Rat at home.
The GT-OD is more like a standard OD, louder by a good bit, still pushes the mids a bit, but nowhere near TS levels, and it isn't as effective at cutting the low end and tightening up. Someone on here says it sounds like a Fulldrive, which I can't cop to, but there you go.
There's a pretty significant difference, and both settings are really good at what they do. Great pedal.