Those two
might be a bit thinner (in HTHSV) than the T6.
I believe the M1 is 3.6 currently and the Castrol is ~3.7, whereas the T6 is at or above 4.0 in
High
Temperature
High
Shear
Viscosity, so they will be slightly better than the T6 in that regard, but still much worse than even the thickest 0W/5W-20s out there.
Most of the year (save for the occasional cold snaps) in mid-southern Florida, the difference will not matter at all.
But what I do NOT know (maybe a Ford tech/engineer on here can confirm this or not??) is IF the variable valve timing, and/or cam phaser mechanisms (<-IF we have those??) in these 1.6 EcoBoosts
require a certain viscosity to function properly, as is necessary in other engines/brands with VVT/CP/etc.?
IF they do, I would not go too high above the required viscosity, unless for open tracking/road course use in the summer, where it will shear down quickly to about a 20 weight's HTHSV range (~2.6-2.9) anyway after a couple of laps.
I'm guessing the answer on whether or not we can safely use higher viscosity oils would be IF the Antipodes/Southeast Asian/Middle Eastern (or any other HOT climate) sold FiSTs say that they can (or even SHOULD above certain ambient temps) use 5W-30s (or even thicker) oils right in their manuals??
That is,
unless they use a completely different VVT system in their engines (VERY doubtful about that!).