OldNeumannTapr, the Neumann KM 140 can handle 138 dB SPL without the pad--and Neumann tends to specify things in a conservative way. So I really, really doubt that your microphones--themselves--are being pushed into overload if you're powering them properly. Based on what you wrote, I think that you'd probably agree. And in an emergency, using the pad switches on the microphones may be your only available solution. No dispute there.
But once you realize that your "downstream" equipment--your preamp, mixer or recorder--is at risk of input overload, then if that downstream equipment has no setting that fixes the problem, you need to use balanced, in-line resistive pads at the inputs of that equipment. Those are available from all pro equipment dealers. Shure makes them, Audio-Technica makes them, Whirlwind and many lesser brands offer them as well for less money (e.g. ~$20). They're very good to have in your bag at all times. I'd suggest a pad value of 15 or 20 dB for typical situations (technically 12 dB is the minimum for ideal impedance relationships, but if 10 dB floats your boat, so be it).
And then turn your microphones' pad switches off, and leave them off! Unless, as I said, you have a situation in which the microphones themselves are in danger of being overloaded--which should be exceedingly rare; 138 dB SPL causes severe hearing loss within minutes.
The reason this is not just a "matter of opinion" or "personal preference" is that using the internal pad in a condenser microphone reduces the output levels, while the self-noise (noise floor) of the circuitry remains the same. The pad switch works "early on" in the circuit to prevent the capsule's output from overloading the first stage of the amplifier, i.e. the FET or vacuum tube. Thus, relative to the signals that you're recording, the noise floor of the microphone goes UP by the same amount, e.g. 10 dB, whenever you throw the switch--and the noise floor of your microphones is distinctly greater than the noise floor of the MV 100 preamp. Your recordings also become 10 dB more vulnerable to any interference that's being radiated into the cables.
By comparison, a resistive pad at the input of the preamp, mixer or recorder will reduce BOTH the signals (that threaten to overload the device) AND the self-noise of the microphone AND any induced interference all by the same amount--thus preserving the full dynamic range of the microphone's signals, and reducing noise due to any interference.
--best regards