Just a few thoughts here; First the blasted chart! Mil Spec hill stichk! I remember not that long ago the "TDP"(Technical Data Package) that gave all the mil-spec requirements for a real military M-4 found its way into Bushmasters HQ! The stink was over them stamping M4 on their ARs, Colt sued over the rights to the name and LOST!
Second; FN is the one building the majority of M-16 A4s and A4s for the military, Colt WAS building the M4 until just recently when Remington got the new contract!(Yeah my heads still swimming over that one!) Remington owns Bushmaster at the moment so we know who's building M4s now.
Third; barrel twist 1/7 was ordered by the Marine Corp when the new A2 rolled out. They wanted a heavier bullet so they could hit out to 500 yards, plus the old 1/12 wouldn't stabilize the M-856 tracer round. Plus the recent introduction of the 77gr. OTM OR Mk.262 round demands the 1/7 twist.
As far as I'm concerned we're not going to be hunting terrorists or assaulting fortresses any time soon. We buy ARs for the sporting purposes (and self defense)and the accuracy of said system is there for varmint and predator hunting. 1/9 will handle the majority of bullets out there unless you feel the need to go beyond say 69 grains, and I've heard nothing but good things about the 1/8 5R barrels too!
What do I have? At the moment a Mini 14 580 series, and a SIG 556, but I like being different.

If I were to buy an AR today I'd look hard at the Smith line up as well as Windam Weaponery they are the old Bushmaster after all
And that PMC 55gr. "X-TAC" is good stuff, buy cheap and stack it deep! Dale