Indeed Pym! The optimum force is eight 139's/149's in order to have a deployable four-ship detachment. But there is no rush, other than fears of the government changing and/or losing interest. It will take the next several years to fully absorb the new capbilities of the 139's and grow fully qualified tactical helo crews. They don't even have FLIR systems installed yet.
Two more orderd early in 2007 will be for delivery in 2009, maybe even late 2008 unless they are 149's, in which case delivery is probably not likely before later in 2009 or even into 2010. A final two ordered in 2008 would be delivered in 2010 or early 2011. Probably about the right rate of build-up for the IAC from this point, and the right spread of expenditure.