I see the 27 as a CCW primarily, not a duty/battle handgun. That means concealed under clothing possibly IWB. That means the RTF against your skin, either rubbing you raw on your bare skin or eating up your shirts. It will abrade clothing eventually and eat holes in your clothes, its simple physics. The Gen 4 also has removable back straps.
So if your hands fit it fine, go with the gen 3.