. . it's flow that matters, not pressure. Oil pressure isn't what keeps the bearings and crankshaft apart, it's a wedging action from the viscosity of the oil. Compared to the mechanical pressures oil pressure itself is insignificant.

I've had plenty of cars that had low pressure at idle but kept on going for many years. I don't know at what pressure your light goes on, but I've heard of cars getting along fine with about 6 pounds of pressure at speed, though I prefer at least 12 myself.

10/40 oil is good, I've never resorted to 10/50 but it does exist and might prevent your light from going on, particularly if the problem is a worn or out of spec. oil pump.