We are to develop a social networking kind of web app for our and our clients' employees. The number of users can go high. My question is which platform would be better for this project, considering performance speed as the main criteria and faster development as the second criteria. php+mysql or .net+msmql or java+oracle. I would like to know why.
Note: We have good programmers in .NET and php.. We are ready to recruit java programmers if necessary. Please advice.

Performance speed in these cases is usually defined by good database design and server management, and caching (query and output). I'd suggest you use the path for which your team has the best skills.