I spent some of my lunch time playing with the jumper and comparing the two pedals. I was not able to figure out what the jumper is changing. I didn't hear any difference in either of the sides of the pedal as far as tone and gain. That is going to be a mystery for a while longer, maybe forever.
As for the comparison of the two pedals.
I was able to make side 1 of the PD sound like side 1 of the Gearbox by setting it to soft clipping and the lowest gain level setting.
I was able to get side 2 of the PD sound like the side 2 of the Gearbox by setting it to hard clipping and middle gain level setting.
They were very close with these settings.
There is a little bit more mid push in the Gearbox channel 1 than the PD channel 1 with these settings. However, the tone controls on both pedals are very powerful and I was able to get them adjusted so close that you would never tell the difference in a band context.
The PD is more configurable and has a wider range of tones in it. The PD has soft clipping, hard clipping and mixed clipping options. It also has 3 levels of gain structure. These are options on both sides of the pedal. I didn't test to see how they do at max gain. They both have way more gain and bass than I will ever have a use for.
The Gearbox has a very nice noise gate on it. The PD does not have this feature. If having a gate is important to you, be aware of this. It works very well.
The PD has a master presence knob. I am not sure if I consider this a strength or a weakness. I understand it is to match the pedal to your amp. However, I would have liked it to have a presence for each side so I could set them different from one another. That would add more tone shaping ability to the pedal.
I like having the clipping and gain options in the PD. I don't know if it was an intended feature but I hear a difference in the midrange response of the pedal when switching the clipping types. I didn't expect this. I am wondering if there are some intended differences in the circuit to do this. I just expected to hear a difference in the clipping itself and not the tonal characteristics of it.
Both of these are fantastic sounding pedals. I do not regret buying both of them. There is enough difference in them that I will get use out of both. One of my next comparisons will be to put them up against The Engine by Drybell that I bought several months back. This pedal really impressed me with the first note I played through it.