When my car was new in 1975 my dad read about the new fangled Mobil 1 synthetic, up until the he'd used 10W-40 Conventional oils and living in Northern Finland he complained that his car cranked slowly in the winter ( -30C is not uncommon there ), so he went and bought the expensive Mobil 1 ( 5W-20 only at the time ), and apparently he liked it, he said the engine cranked over a whole lot better, which is no surprise, he continued using it for some time until the engine no longer could maintain a good oil pressure with the thin 5W-20 that it was not designed for, so after that he used various 10W-40 and 20W-50 Conventional oils, and also he got a heated garage so it wouldn't be a pain to start in the winter.
The in 1980 my family moved to Spain so thin synthetic oils weren't needed so he used various 20W-50 oils, then in June 1991 in Germany the original engine blew up because of the common fault with old Ford engines of the hexagonal shaft that drives the oil pump, it broke and lost oil pressure and the engine was toast, he went in to a Ford dealership in Karlsruhe, Germany where they put in a replacement engine, after that he moved away from 20W-50 oils and switched to 10W-40 oils because he had been told that the thick 20W-50 had caused the failure ( probably not as the manual states it's fine in hot climates ) , and he continued using that until some years ago i got the car, i contunued using 10W-40 synthetic blends until now, and now it's back on 20W-50 Dino, thinking about trying M1 5W-50 or Valvoline VR1 20W-50 Dino.