SSRS является довольно медленным когда дело доходит до генерации отчетов. Настройка T/SQL о лучшем, которое можно сделать.
I would imagine the file system cache would handle this in much the same way it handles all of the other files apache has to open. If you're planning to replace an active site with a check for a single file, then you shouldn't have to worry about the performance hit.