You must have access to oscilloscopes then? I'm sure you can design a test amplifier circuit where you can measure the impact a wire can have on the entire design. Have the oscilloscope point between the two outputs and see for yourself if the wire did any damage for your circuit. My experiences with this is that there is no impact of introducing a wire whatsoever to an amplifier circuit.
I do have access to oscilloscope but prefer to use my ears to judge sq differences.
I'm sure that in simple wire breadboard design extra 30-40cm of metal wire doesn't make huge difference, but again this is a little more complicated design.