Microsoft ACE team has been involved in performance testing and tuning of web applications within Microsoft and externally for several years now. Microsoft's
Information Security - ACE Performance has been using a methodology which they have now formalized as PDL-IT (Performance Development Lifecycle for IT) which consists of a proactive approach for application performance within the SDLC.
Irfan Chaudhry, Director of InfoSec's ACE Team, explains this methodology after being part of ACE for 8 years and having started as a Performance Analyst himself.
If you want to learn more about PDL-IT, you can read more on the ACE Team blog in a series of posts.