1. Amen on the motorcraft filters!
2.Why mix weights?
3. I use straight 10w30 mobil 1 in the motor now that its blown , but have used 0w20 mobil 1, in the past , but its all the same sorta ....long chain hydrocarbons engineered to give max sheer and pressure protection.... most of the diff comes from viscosity modifiers added to the synthetic brew... and all that changes is flow. The greater the difference in the numeric values, the more viscosity modifier you get, so 10w30 should be as good as anything, but back in the old days, when multi viscosity oils started out, they had a lotta probs in S. Cal. due to oils "gelling" in verry hi temps, go figure.... I think a straight 20 mobil 1 might be thev best of all , but hey, what do I know?.... been useing Mobil 1 since about 1970 when it was first introduced as an experiment in the midwest, and it has never failed me..