5-10 years ago the answer was…yes to the first question as the second one didn’t apply.  As I have been watching the evolution of hardware over the years things of course are more complex.  In a nutshell going with a low power server(or maybe a desktop CPU for workstation users) actually harms performance more than any increased power.  In fact with the newest CPU’s from Intel(AMD is a bit behind) running Windows in the “Balanced” power profile actually HURTS both power savings and significantly inhibits overall performance.  One the desktop the roles are a bit reversed…the absolute power savings most likely would be worth the performance hit IF you aren’t worried about complex, real world tasks(like real time rendering, financial analysis..etc etc etc)).