I appreciate all the input. I haven't even seen the Miata in person (on line purchase) and am way out of my league on this stuff. In the interest of full disclosure, my son is an engineer with ExxonMobil, so we are definitely biased when it comes to oil and oil filters--Mobil 1 all the way!
I use 0W40 in the 2015 VW Golf TSI, 0W20 in the 2010 CRV. Of course, those are driven in the sometimes sub-zero winter days in Northern Wisconsin, while the Miata is strictly a May to October vehicle. So, the "thicker"oils approach does seem to make some sense to me. The recommendation for the stock model is 10W30.
Smart guys, keep the answers coming! I do appreciate the wisdom of the car enthusiasts out there.