you can expect a small loss in fuel economy and a slight loss in power due to the parasitic loss to the higher fluid friction in the thicker oil.

I'd expect the engine to feel smoother in the upper revs.

I'd be hesitant about using this oil in cooler weather becasue the oil galleries of the engine were designed to accomodate a multigrade SAE30 oil so when the oil is cold and thick it may take an excessive ammount of time before it reaches certain areas of the engine after start-up.

I feel sorry for the people who don't drink. When they wake up in the morning, thats the best they're going to feel all day - former President Lyndon B. Johnson