I live where it's often colder than Mars. I'm sticking with Mobil 1 until Walmart realizes California isn't the world.
It gets well under -200 F on Mars, you must be in quite a place.
I demand a pour test on Mars between Supertech 5W30 and Mobil 1 5W30!
Walmart and Exxon could easily afford a Mars lander and robot that could unscew the lids and turn the two bottles upside down over a recycling bin while recording video. (Keeping Mars litter-free for 4.6 billion years!)