On the OEM question: Probably, but I've had new Remington 243 barrels vary between 9 1/8" and 9 7/8" twist as measured by yours truly. The latter of the two wouldn't shoot them well.
I'm of the same opinion as Bowhunter and Dude in that my new 6mm creed would be 1-8". I have one currently that is 1-7" and it shoots great. My buddy has the same brand barrel, twist, and chambering, but at 800ish rounds it is doing weird stuff with 105 grain bullets at the speeds that he has shot from the beginning. We think the bullet jackets are being degraded some now that the barrel isn't "new". He's at something like 326k rpm in the 1-7" barrel, where a 1-8" would put him at 285k and still easily stabilize the bullets that he's shooting.
I'd have to think about it long and hard, maybe do some math, but a faster twist in 6.5 might be useful. Bullets are still getting longer and the lower velocity would make rpm concerns lesser. 1:8 was very fast for a .224" a few years ago; now I'd be looking at 7 for a new barrel.