I have a 16" bull barreled DPMS that will shoot every thing from 50gr up to 64gr very nicely... I could probably go even heavier, but just haven't had the need..
My other AR has a 1/14 twist and shoots 35gr - 55gr in small groups..
IMHO, the 1/9 is an extremely versatile twist rate...especially in an AR...
Not concerning mine,,,,, I've shot several 3-gun competitions at the "big money" matches ($160k on the prize tables) as well as locally and never had a 'hiccup', it feeds from most mags, and is accurate enough for most 200yd egg shoots...
I'm not saying that any other brand is better, or worse, since I've had very little experience with most of the other factory brands...