PHP sites

I am not sure if this list is the place to ask this question. I am the president of the OpenEMR development group. OpenEMR is a free open source electronic health record that is being looked at by increasingly large vendors in the United States because of the recent HITECH portion of the US Economic Recovery and Stimulus Act of 2009. We are starting face issues of scalablility and would like to provide a list of high volume sites to answer our critics about the scalability of LAMP stacks. I am looking for resources or a list of sites that are very high volume PHP sites. I was hoping that you might direct me towards the appropriate resource? Sincerely, Sam Bowen, MD OpenEMR Open Source Medical Software