I've simulated both the Juno 106 filter (with 270pF caps) and the JP6 filter in 24dB LP mode, to figure out their response - what voltage (or rather current) to frequency rate to expect.
Quite interestingly, the two implementations track each other fairly well. Both have around a 30Hz per mA or 30uA per Hz response.
EDIT 26/12-18: It seems I've messed up a bit? (0.1V / 3300Ohm ) / 4 is not 7.57mA, it's 7.57uA. Thus the response is 30Hz/uA or 30nA/Hz?
Also very interesting to note is that the response is not linear. The higher the frequency, the more current is needed for the same change in Hertz.
I measured the 3dB point at 16 selected currents:
The CV is the input to a constant current circuit. It is the voltage across a 3k3 resistor, and the resulting current (buffered to stay constant) is split between the four cells of the filters.
I selected 8 tightly spaced voltages and 8 further apart, as the lower end requires less change to double the frequency. Deltas are the difference between two measurements. F_c is the 3dB cutoff frequency point. This is a linear CV, e.g. without the exponential converter connected.
The result ended up like this:
So what does this mean? It means that the V/oct tracking of the filter is not perfect. It will be slightly more closed as one moves up the scale on the keyboard. I have read about this effect earlier, and the writer noted that it didn't seem to matter all that much. I guess a little difference is hard to hear when the base frequency changes a lot.