Assessing the performance of your site will typically be one of your tasks as a system administrator, project manager or developer before delivering your final product.  Establishing a goal for performance such as load time and concurrent users is common for evaluating the load a server can continuously deliver without flinching.  However, not all sites are created equal.  The overall performance will be impacted the most by the most recurring visit profile, i.e. how the site is actually used the most.