Ed, you've got a Mesa Studio Pre, too? Awesome… that's been my favorite "amp" for 18 years now, and the first amp I ever owned in my life that I didn't hate after 2 months. I still love it! Anyway…
You've got a point about delays after distortion… however, I actually really like what a good analog or tape delay sounds like in front of a Marshall (or similar). The repeats get cleaner… good for Live at Leeds type sounds. EVH may have used an Echoplex in front to boost the gain… I know that's greatly debated. None of that really applies to the PF, though. Not really the TF, either.
Sometimes (not always), the PF shifters track better in front. There are fewer harmonics and less compression, both of which are added by distortion and can throw off the pitch detector. The PF has a smoother sound overall in the loop, though.
I think a lot of it has to do with how much distortion, you know? Overdrive… crunch… high-gain… insanity…
