In this study, we investigate the role of configurational entropy on the room temperature tensile deformation response of single crystalline medium/high entropy alloys (M/HEAs), in particular in terms of activation of deformation twinning with and without interstitial carbon addition. In addition, we compare the strain hardening behavior and ductility of these materials with that of conventional steel single crystals. TEM observations revealed that two deformation mechanisms govern the strain hardening in M/HEAs, namely planar slip and twinning. It was observed that nanotwin formation was prevalent at the early stages of deformationin in almost all of the above M/HEAs, significantly enhancing the ductility, while the higher strength levels are associated with the high volume fraction of thin twins. Overall, it was concluded that higher configurational entropy does not neccessarialy warrant improved mechanical properties, as the mechanical properties of NiCoCr, SS316 and Hadfield steels are comparable or better than their HEAs counterparts.