We re-assess the reach, at a 100 TeV proton-proton collider, for a heavy particle that decays only to MET, under varying detector properties. We analyse the sensitivity to a charged track stub due to the production and decay of a high-momentum electrically-charged component; and also independently to additional radiation from the initial state of a hard leptonic $Z$-boson, and ask what tracker and calo specs will be necessary to extend the reach to larger masses/shorter lifetimes than might be possible at an ATLAS/CMS-type detector.