I recently have a data import slowness issue reported taking days to process without finishing even in batch run in parallel. This issue could occur with any entity import especially for new company go-living or with no data in the target entity.
I recently have an incident with the same timeout error mentioned in the blog in below that customer would like to run report exceeding 4 minutes in EP. The same steps are used to extend the AsyncPostBackTimeout attribute except that AxScriptManager is searched/modified instead of ScriptManager in the master page mentioned in the blog. http://blogs.msdn.com/b/selvar/archive/2013/05/15/sharepoint-web-part-page-hosting-reportviewer-web-part-fails-with-sys-webforms-pagerequestmanagertimeoutexception-the-server-request-timed-out.
