[reduce power consumption (electricity)]

Have you seen actual results in saving electricity in the mentioned specs?

[5000 years ago Sahara was a green landscape with lakes and rivers]

So much has changed over the last 5000 years. One wouldn't recognize it for the former appearance.

[I'm Planning to Get a New PC and I Need Advice]

I would wait a bit longer, save more, and then get a better machine with more power.

[Age of Empires 2 Definitive Edition]

Definitely the best game ever made.