SharePoint 2007 "Farm" Sizing

Yesterday, during my GeekSpeak webcast (Which was fun by the way) the question came up as to how many SSRS instances could be supported per SharePoint farm. I kind of stumbled through the question and didn't have a very good answer, so I spent a little bit of time yesterday researching the topic. Unfortunately I don't have a much better answer to post here today, but one thing that comes to mind is that there is a clear statement from Microsoft that there should be 1 Database Server for every 8 Web Servers in a farm. (See the Microsoft SharePoint sizing recommendations here: http://technet2.microsoft.com/Office/en-us/library/6a13cd9f-4b44-40d6-85aa-c70a8e5c34fe1033.mspx?mfr=true )

So, using the ideas in the document above, and understanding that there can only be 1 SSRS instance for each Web Server, and "taking a bit off the top" for the overhead on the database server that an SSRS instance will generate, I'd say you should modify the recommendations slightly and say that you should limit SSRS integration to 5 instances of SSRS per Database Server in the farm. (This is in no way an official limitation, it's simply conservative extrapolation on my part)