I'm not up to date on the Armalite stuff. Last I had heard, I thought they were discontinuing the .243 and the other less popular AR calibers. And trying to get a .243 magazine for it if available, iirc they were expensive. A friend of mine has the .308 Armalite and the modified M14 mags were out of site pricewise; nice rifle though. I'm sure the .243 AR would be a nice gun; I just think the Grendel would be a much nicer rifle now and long term. Long range the Grendel will beat it hands down.
Wolf is supposedly going to put commercial ammo out on the market late Spring-early Summer; brass case, quality ammo from the Serbia(?) plant (noted for quality), and the price will be much better than the current prices. Typically, if you're a varmint hunter you reload. But the Wolf ammo that will be coming out should make that optional too. Go to http://www.65grendel.com/ you should be able to find some ballistics on it there. The Grendel will be coming into it's own, this I'm sure of. I have a 24" Overwatch, think Varminter, it's a tackdriver short or long range. It is very nice to shoot also. Pricewise; buy once, cry once.
eta: Glad they got the price down on the .308 mags. After the SHOT show, it was announced that Armalite will be offering Grendels also.