From the viscosity number I get Synthetic is thinner so I did some math.
You mean at -35C? Otherwise this makes no sense.
Viscosity in the oil ratings system is a range of measured values. There are theories about flow characteristics of syn, but that’s not measured in the viscosity rating, at temperature.
You mentioned operating hot and cold, but are you routinely encountering far below freezing? If not, your math is suspect, because it’s just a measured value.
I think as others have said, find a light 30wt oil and run that.