Laptop more battery efficiency vs best performance?

There are two variants of modern laptops. How much% is the performance better if I have the battery mode on "Best performance" instead of on "More battery efficiency".

Depends on the setting. You can take that pretty far. E.g. Max. 60W vs 12W.

The more power a notebook has, the more you can save.

With a system that consumes a maximum of 20W, you can't save so much with a minimum of 12 W.

I clock my laptop from 3.6Ghz down to 0.9 and double the time from 4 to 8h. What if that happens. Gets a little slower, but works