I am about to start the journey to build a niche social network. It is a bit of learning experiment. I would like the site to be able to scale because the niche has a lot of potential. I am thinking about 25,000 to 100,000 logged in users concurrently, if the website ever became popular. If I am mainly concerned with getting the best performance and scalability for logged in / authenticated users, would it be better to go with C# and .Net or PHP?