Taylor, journal diameter, width, clearance, load and speed all relate to actual viscosity of the oil, not greatly to the HTHS.
I've seen some 21" diameter, 19" wide 3,000RPM bearings that will have a 500% increase in vibration with a 2C change in oil temp (viscosity change).
ArcticCat, speed is not always your friend, and it can reduce bearing stability criteria.