I see no reason to switch to anything less than a 40 or 50 weight...  what
you're after is better cold starts?  Note that the second number is the
viscosity rating once the oil is up to operating temperature.  I suspect you
don't want to run a lighter weight oil at operating temp than you have to.

I think I saw a 15W-50 mobile 1 product.  That sound pretty ideal to me..
I'm running 15W-40 amsoil at the moment. Next year I intend to try to 20W-50
year round.  For whatever reason, I'm sold on amsoil. We'll see how it
behaves though.

From my understanding, you never want to run a w-30 oil ever.  And 40 isn't
as desirable as 50 for these beasts.  I suppose it's the viscosity spread
that you're concerned with?

Brad