Originally Posted by Smokey Bear
If the oil takes longer to get to optimum temperature then more wear is occurring on the moving parts. Oil is a trade off. Better characteristics at high temperatures means a trade off at lower temperatures.
Just because you have a ten w on the bottle doesn't mean 10w40 will perform exactly the same as 10w60.
Yes it will fall within the "spec" for the 10w number but it won't perform exactly the same from startup.
So yes the oil is made to work hard at high temperature but it's not the best oil for startup and heat up of the engine.