Actually, what AC and GS are saying is really the same thing in a lot of ways. In my post on M4C that AC links to you'll see at least one poster suggesting getting out to classes and matches as a way to try out other folk's gear and see what works for you.

and it all dovetails nicely into the point of this thread, which is that you can get 98% of the way "there" with only three additions to the carbine (outside of the obvious ammo, mags, training).