Hey GS:
I run Mobil1 5W-30 year round. I have no pressure problems (50+ in summer at idle). I know there is a love affair with 20W-50 with these cars, but it's a mistake. The thicker oils do not make the trip through the long lines, the filter and the cooler very well.
Prove it to yourself. Take a few ounces of 5w-30 Mobil1 (or whatever
synthetic) and your everyday 20W-50, put them in a couple of glass bottles and put them in your freezer. After a couple of hours take them out and compare the viscosities. If this does not convince you then so be it. When I called Ford Motorsports they told me to use 5W-30 all year round.
Also, can we leave the scripture to another forum
Bob