How to Determine Most Efficient Tire

[Ecky]

I've gathered that tyres sold in NZ and tires sold in the US aren't necessarily the same, even if they have the same name and model number and size.

I often go to https://www.tyrereviews.com/ for numbers. Often they list RR values. I believe these are measured, and will vary from test to test, but if you read a bunch of reviews that include the same tire, you can get a general idea.