So what I got out of the web page you supplied is that 5w is 5w at -30 and that is the same for either Oil or Synthetic.
Both have the same viscosity and -30
5W-50 3,500 @ -30 30,000 @ -40
5W 3,500 @ -25 60,000 @ -35
As with all multi-viscosity oils or synthetics as they heat up the viscosity changes and the oil gets heavier.
At temp the 5w-50 is 5w when cold and the vis raises as the temp goes up till it hits 50w?
The low will not get any lower than 5w and the high will not get any heavier than 50w.
Did I miss something?
Thanks