Vlad I left it a bit open, not being sure of the relative performance / battery implications of some of these settings, but to take a stab (in the dark!):
On Power Adapter (i.e. optimising for slower Mac or network)
- Enable Content Blockers
- Block Web Fonts
- Enable Javascript
- Enable Reader Mode
On Battery
As above plus:
- Enable Low Power Mode
- Enable Low Power Mode when battery reaches: (slider with battery levels in %)
Finally, I guess an "extreme" setting to optimise for slow networks might be to block the loading of images, but that might be going too far…!