My opinion - keep the SIG M400 and buy a Service Grade Garand from the CMP for $625. Get the 1911 later.
Right now, the M400 and all that ammo (even Tula) is gonna be worth a whole lot more than a Garand. But, who knows in 6 months if you'll be able to get another AR if you change your mind? Likewise, the CMP has stated that they have about 2 years worth of mail-order Garands left. After that, expect used Garand prices to rise considerably.
On the other hand, it's a good chance you'll be able to find nice 1911s for a long time.
Last edited by Fishbed77; January 15, 2013 at 12:04 PM.