I (manually) generated 500.000 visits during yesterday for the same site. Piwik has worked very well and very fast (2min30 with a cronjob), except the Actions’ part, where the first page’s URL visited counted only 250 views …
Today, I will generate 10.000 fake sites and a maximum of visits for them.
If you have any advice for my tests are as close to reality …!! style_emoticons/<#EMO_DIR#>/wink.gif