What is behind your question? If there is a concern about performance behind your question, then there might be good reason to performance test. Regardless, performance testing should be required for any system or application. I think it would be best for you to seek answers within your organization and from your customer base. Please be sure to include people with a strong knowledge of the system architecture and those with a strong knowledge of performance testing and engineering.
Also, measurement of "a web page" might not be adequate. It would be key to establish the questions about performance needing to be answered.
Not sure if this is relevant to the original question or not, but we are frequently asked to determine if a new release of an application performs "better" or "worse" than the previous release. If we have load test results that are still relevant for the AUT, then we can use them to compare. Often, we've had to design our tests to include scripting and execution against the old version as well as the new version.
SoCalGal - Defender of end user response times!