The speed of your website load time and the number of concurrent users will be dependent on the complexity of your website, the number of media elements loaded through the web browser, the total weightage of all media elements including other supporting elements such as javascript, css and DOM components, as well as the optimization database write/read/store structure and processing.
Ultimately, if you were to put a single index.html page, you will be able to achieve an extremely large number of concurrent visitors coming in to your web server. However, if your website is complex, the number of concurrent visitors can vary accordingly with the complexity of your website.