AR Performance makes one of the best 16" barrels you can get for under 200.00 delivered.
They also make the super bolt for the 6.8.
The barrel has the 6.8 x 43 high pressure chamber with a 1/11.25 twist rate in medium profile.
My son's 6.8 has that barrel/bolt combo and is the most accurate one we own in that cal.

You will need a different magazine but unless you already have an AR, you need a magazine anyway.
I'm running AR Stoner magazines from MidwayUSA.

Do a google search for 6.8 forum - there is tons of good info over there and everything you want to know about a 6.8.
One of the friendliest no BS forums I've visited and I live on forums.

I've seen the AR Performance site and they have some useful info, but Why do most of the 6.8 barrels I see have a 1/9 twist. I saw several at the gunshow yesterday and didn't buy because of what I'd read on AR Performance

So what is the "ideal" Twist rate on a 16" 6.8 barrel? All of this info has me leaning toward 6.8 and not the other that I started with.

On a 6.8 no matter what the barrel length I would go 1-11

http://www.ar15performance.com/6_8_arp

Hands Down!

So these heavier bullets don't need a Faster twist than a 5.56?

I've had a 6.8 and now own a 300 BO.

I can say while I've never shot a deer with the 6.8 I did put down a few hogs with it with ease. Loved the round.

Right now I have a 300 BO and just took several deer with it this weekend. Using Barnes Vor-tx ammo I dropped one doe where she stood and shot a buck that went 50 yards before falling. Both were through and through shots at 80-120 yards.

I really like my 300 BO compared to my 6.8. Ammo is about the same price but you can find 300 BO plinking ammo much cheaper. The BO kicks a little less tho both are nothing to worry about.

Can't go wrong with either IMO.