The narrowest allowed console window, in pixels, on a conventional (~96dpi)
monitor:

(mode con: cols=40 lines=40) && SetFont.exe -face "Lucida Console" -h 1 && (ping -n 4 127.0.0.1 > NUL) && cls && GetConsolePos.exe && SetFont.exe -face "Lucida Console" -h 12

(mode con: cols=40 lines=40) && SetFont.exe -face "Lucida Console" -h 16 && (ping -n 4 127.0.0.1 > NUL) && cls && GetConsolePos.exe && SetFont.exe -face "Lucida Console" -h 12

                sz1:px      sz1:col     sz16:px     sz16:col
Vista:          124         104         137         10
Windows 7:      132         112         147         11
Windows 8:      140         120         147         11
Windows 8.1:    140         120         147         11
Windows 10 OLD: 136         116         147         11
Windows 10 NEW: 136         103         136         10

I used build 14342 to test Windows 10.