So it means it doesn't make a difference unless you needed the power?
May or may not. This because equipment design and components are different. And then even if they are within the same series, design do differ between models. Take the krell fpb series for eg. The fpb700cx is very different from the fpb300cx.
Since higher power are usually associated with being higher end (more expensive as well), so deisgn and selection of components may not be the same.