Good point with #4. The last time I was involved in a Microsoft project the SQL Server licensing costs were more than $30k per box. $30k was not a big deal on that project but it would have worked a lot better if the data had been spread across a bunch of little servers instead of two big ones. $30k * 2 is not so much; $30k * 50 starts to add up.

http://www.microsoft.com/sqlserver/2008/en/us/pricing.aspx