I spring for Royal Purple in my supercharged, 7k RPM redline 4.6L DOHC mustang. Even in that engine I think it's overkill, but then I only change it a couple times per year so the extra cost isn't a big deal. Is there a benefit? probably. It's hard to say. I know that one tends to get a lot hotter and spin a lot faster than my 3.5L. I like having the peace of mind knowing that if I break it, the oil wasn't the problem. I do plan to run conventional in the 3.5L for every single oil change. I'll spend a bit more on the filter, but IMO there's no justification for the really expensive oil in this engine.

 

5w20 motorcraft syn blend in my 2002 f150 219k and counting.
5w20 mobil 1 in my wifes 2007 freestyle. 104k and counting.
10w30 royale purple in my 89 mustang. 347 with all the goodies.
all run standard motorcraft filters.