Thank you.
Additional vehicle and driving style info:
I have the DOHC 5.0L with re-programming by Ford Racing. The mod increased torque off-idle by 60 lb-ft!! It delivers 440 HP and 400 lb-ft. with my exhaust mods. Redline is 7,000 RPM. Crankshaft is forged steel. Pistons hypereutectic. Suspension mods too numerous to list here, but car has FRPP integrated package and lowers the car 1.5". Torsen 2R racing differential added. Barton shifter. Diff uses MC 100% syn 75w/140. Tranny uses formulation Molakule developed years ago for the S2000. Engine has oil to liquid cooling and tranny is air-cooled with an additional flow diverter.
So I have made this into essentially a Boss 302, with more juice down low less power in the last 500 RPM or so. Prefer my suspension so I call mine the CEO 302.
So what? Well Ford now labels a Track Package which has pieces I already added. Then there was the Boss 302. These come with a 5w50 recommendation. Huge diff between this and a 5w20, no?
My car is fast and does its work with tremendous mid to upper mid power, and a torque curve as flat as Kansas. I do some hot laps full bore at Virginia International Raceway a few times a year, but most driving is back road blasts. Always with long warm-ups and cool-downs. Garage is heated/air-conditioned. 2,700 miles.
I believe that fast start-up flow is a key performance indicator of quality oil. So the lower the initial vis, the better. But my ME was based in part with tribology, and maintaining film strength at sustained RPM is another KPI that counts in my book. So I used Syntec 5w40 Euro-spec at my first change, and now want to choose a vis to cling to (pun intended). Hence my question and suggested recommendations. Thank you. RR.