Does using an expensive oil make a difference ?

Valvoline my 5.0s drink of choice... drink because thats what it has a habit of doing(fixing soon heh). I ran mobil 1 in my steed for a couple changes this last year for a total of 4k miles. I noticed that it DID run slightly cooler, but only on the hottest days. IMHO its not worth it unless its an extreme/very high performance application.