I've got a Chopper in the middle position of one of my PGMs and a Pro Track in the other.
The PGM with the Chopper for one PGM has a Humbucker from Hell in the neck and a
Tone Zone in the bridge. I chose the Chopper for this guitar because for tonal and volume balance when switching across position. I got get some decent Strat-ish sounds (positions 2 and 4 on the 5 way) with that one.
My other PGM has a PAF Joe in the neck and a Tone Zone in the bridge. The Pro Track balances well with those humbuckers.
I also just ordered a Chopper for the
neck position of my new Charvel because I wanted an pickup that would offer good articulation with distortion.
I believe quite a few folks like the Chopper in the middle because it's a good compromise between a plain single coil and bucking the hum when it's used alone. While it doesn't sound quite as Strat-y as the original PGM middle single coil, it's good enough for me.