I own a CAR 4 from RRA, you'll be happy. The trigger work is excellent. (Then again these two brothers used to work for Les Baer, so it should be).
I've been considering building another upper to use with it, in a non-standard caliber. I found out Olympic Arms will provide a complete upper in the 500-600 range. So keep that in mind in the future when you get a hankering to get a gun in beefier caliber. The other cals to consider are:
.300 Whisper/Fireball, can be loaded supersonic, or subsonic and still pack a punch.
.458 SOCOM, great short - medium range hunting slug.
6.8mm Rem. SPC. Keep you eye on it.
One of the guys who runs the local gun range here was down at the show in Nevada a couple weeks ago. He said there was a fair amount of talk about the caliber. And I know Barrett has been working on an upper in this caliber for quite some time. BTW, all these calibers will allow use of standard M16/AR magazines, so we got that going for us also. Which is good.