First of all make full use of the software you hvae.
What is you objective?
I know that sounds like a dumb question, but what you intend to do makes a difference. If you want to do a slide show, the performance requirements are low and there is little need to improve performance.
But if you objective is to see how fast the computer can perform a complex math function, the requirements are different.
Also, with modern technology there is a relationship between speed and the use of power. More speed means more power. Nut if the speed was not needed to perform a task inside a time frame, then the efficiency is said to be lower because the extra use of power was not needed.