Aren't page size and page speed (and energy consumption) correlated? If you request a 1mb page and a 1kb page from the same server, the 1kb one will load faster in basically all scenarios

If you can test speed close to the requester geographically, it's possibly an even better indicator of energy usage because it also implies the data doesn't have to travel as far.

Also, Google has no idea what external resources your browser has cached locally.