Mobil 1 15W-50 has worked for me in the past. I have a '90 Miata with 238,000 miles. It consumes no oil between 5000 mile oil changes. It has had M1 15W-50 from the time it was new (after a 2000 mile break-in). The last belt change was at 180,000 miles, and wear patterns were just visable on the cam lobes. I do not have a UOA, as I am a new member to this forum. Unforunatly, the Miata is being sold to a co-worker, as I just purchased a new RX-8. My other Miata, a '97, has also had M1 15W-50 in it from the time it was new. I will be able to post a UOA on it in a while, so the forum will have hard numbers to work with. Bear in mind, that I live in Houston, Texas, and have to contend with 100+ F days. Your requirement in the Northeast may be radically different than mine! Enjoy the Miata, and keep us posted!