I am not aware of the SIX standards, but the overall goal when analysing the performance of a Web application, according to Segue, is to ensure that the application is operating with optimum ressonsiveness, stability, throughput and scalabilty.
1) The web application must be stable and robust; that is, it must continue to provide service over a long period of time when it is heavily used.
2) The repsonse time for each web page within an application should be as short as possible.
3) The % of scalable web pages should be as high as possible, optimally 100%.
4) Web application throughput should be as high as possible.
5) The no of error that occur in the web applications should be as low as possible.