Down sides of the M1A over GSR... You will use more ammo up. The GSR, I will go slow. I might shoot it 20 times and be done. The M1A? Pfft... 20 rounds? That's only one mag, I'm just getting warmed up. I also felt the need to have 20+ mags since it's a battle rifle. Instead of a Lepold scout scope, I have a Mk IV. So I spent 3-4 times as much on my scope and rings.
So. Much. This.
I bought a bunch of Pakistani machine gun ammo from the 1990's, in links, and that is the stuff I use for general range use. I find I get pretty trigger happy with the M1A. This ammo isn't particularly accurate...but I'm not using it for defense or hunting, it generates smiles. I have it "magged up" in some cheap Korean magazines which I consider disposable. Again, I'm not using them for defense or hunting, so reliability is not an issue...although they have run flawlessly.
Expat, I have to admit a certain amount of envy for that optic setup...I'd like to see that in action some time.