A/B'ed them a couple days ago. With the pedals set exactly the same :
version 4 seemed to be a little louder and somehow harsher (had to roll back the tone on v4 a little to make it sound like v2). Version 2 sounded sort of darker/sweeter.
I guess there's no way to interefer in a curcuit and not change the sound of the pedal. At least, the two KOT versions are VERY close one another. When I tried versions of the Lovepedal COT50 with a volume knob (both handwired and newer), they sounded significantly different from my one-knob version.