I built both of these with no name brand parts (except the triggers, and the barrels are not too shabby either)
The 6.8 is a hunting rifle, with the right load and round, ethical kills out to 350yards (Although honestly most game is taken at less than 150). I reload so my costs are down and typically get between 5-20 reloads (or more) per round. I primarily shoot Barnes 95gr TTSX and Hornday 120 SSTs for game, although I'm also looking at Noslers Accubond at the moment. It is exactly the same as a 5.56, except it uses a different bolt and barrel. I have 2 other 6.8's but this is my work horse, shoots sub-MOA out to 200 , and is a tack driver at 100, as long as I'm doing my part. The barrel( a 6.8 SPCII 1:11)/bolt is from a firm called ar15perfromance and is melonite treated (as in not chrome lined). Cleans like a dream. The upper and lowers are unimportant as long as they hold parts together. The stock is an Ergogrip F93 - solid as hell and my favorite of all my adjustable stocks. I've already changed the rifle - when I bench rest shoot, I use a bipod - and I've since changed the Harris out for an Atlas. I prefer free float tubes - this one is a YHM Diamond that I picked up for $90 - it does it's job. I will be swapping out to a flashhider - the brake/flashhider is totally unnecessary and just makes it louder than it should be.
The 5.56 has a DEZ barrel and receivers from SI Defense -when you used to be able to buy them directly from them.