The PQ-4 supplies a much different frequencey range than the GE series. As soon as you plug it in you can notice the difference. I suppose after using a PQ-4 would be the equivalent of driving a Mercedes then going back to a budget car.
Simply put, the parameters of the PQ are wider so the low end can be made more prominent. When buying a GE-7 oe GE-6 your parametres are very limited. From what I understand, Pantera type sounds are possible with a PQ.
It is also very senstive to touch. So minor adjustments are more pronounced. That being said, it can turn a Tele into a Strat. The biggest prob I have had with the PQ is finding settings I can rely on.
After having gone thru the under 100 Eq market. I think I am up for a change with that or some sort of booster. Maybe CAE Electronics have good products...
I have (and use) both the GE-6 and GE-7 in my chain, and I prefer the GE-6 a LOT more. it is more noisy, but not so much that its unusable. I put the GE-7 before my distortion chain, and then the GE-6 after to clean it up and give it a better color. Out of the choises, I would definately go for a GE-6 (SS a bonus), but not for that price.