I was deployed in Feb. 2004 to Iraq in DCUs, but with a BDU body armor and an M16A2, just like this diorama. The guys deployed in later 2004 got the DCU body armor, then the ACUs came out around 2006.
Most of the 1st Cavalry Division active duty had M4, but almost all the National Guard and Reserves had M16.
The Striker guys were wearing DCU colored ACU in 2004-2005 as an experimental uniform.