What oil weight with oil cooler
 

In theory it seems to me that with a decent oil cooler than you could run M1 0w40 synthetic instead of the 5w30. Thoughts?

Or is the difference so negligible as to be moot.

This could be partially driven by the fact I have a bunch of M1 0w40 sitting in the shelf of my garage, and am going to order an oil cooler for the new Z soon as I nail down which one.

Mobil 0W-40 should be fine but watch for excessive blow-by and diminishing oil levels with
aggressive driving. This is based on my experiences. I prefer to use a 5 or 10 weight oil and a 30 or 40 final weight depending on oil temps I'm seeing. Look at the viscosity number at 100C to determine which is the better oil. For the record I don't use Mobil One oils anymore in the VHR family.