Saving RAM or CPU?

I use Windows 7 Home Premium 64-bit and I have a good system that can handle DWM/Aero. I never run GPU-intensive programs, watching HD videos is all I do.
Should I enable desktop composition (Aero)?
I'm not using any visual effects except for "Show window contents while dragging" and I definitely don't want them.
When I start the Themes service and apply the Aero theme, RAM usage increases 90 MB.
When I use the PC without DWM, CPU usage increases while moving windows.

More RAM usage means less programs cached (bloated programs open slower),
More CPU usage means slower processes while moving windows (slower zipping/unzipping, less profitable bitcoin mining).

Which one makes a signicifant difference on performance? 90 MB RAM or %10 CPU?

I think that is a very complex question for which there is no one answer. It would depend on CPU and GPU performance characteristics, resource availability, and the applications you run. I also expect that the difference would be very small on a computer such as yours. Both the 90 MB RAM usage (less than 1.5% of the total RAM) and the 10% CPU usage occur only under very specific conditions and may be quite different under typical operating situations.

I wouldn't even try to answer your question.