Yes we are going around in cicles, that link basically says the same as the one I posted.
Say for arguments sake you car ran at 100ºC operating temperature, which is probably close to what it really does run at if the thermostat is ok.
A 10w-60 oil will be thicker at this temperature than a 10w-40, hence it would not flow around the engine as easily. (The hot rating on oils is measured at 100ºC)
They may be the same viscosity at 0ºC (the temperature than the "W" rating is measured at), but at anything above this the 10w-60 will be thicker.
A 10w-60 oil has an optimum operating temperature for about 130ºC, so if you car is running at less than this the oil will not be within its ideal operating range. This will make more drag, heat and wear.
Giulietta 2.0JTDm (170), BMW 120d M sport