In what I've gathered on the 30" barrel, it's main goal with this length is to get a 155 grain bullet to near 3000 fps in order to make it to 1000 yards super sonic. I think it is real popular with the palma shooter's.
That may be part of the goal... lord knows there's enough postings on the Net claiming that its not possible to get a 155 going fast enough without a 30" tube... which I call B.S. on from personal experience with not one, but two different factory 26" barrels (one Remington 1-12" tw, and one Savage 1-10" tw). Heck, I can get a 155 going 2830-2840fps from a factory Savage *20"* tube...

In my opinion, the biggest reason for the 30" tube for the Palma guns is to make the clicks on the rear sight work out somewhere close to 1/4". Even so, with a 30" tube and approx. 6" of receiver between the front & rear sights, its still not exact...

Using a 30" barrel in .308 will generally not have a fast twist rate like 1.10 because most will be using that 155 bullet that won't require a fast spin to stabilize it.
Mmmm... my observations on the firing line at various 'big' matches both locally and on the national/international level is that even with the recent trend away from 155s to 185s or 200-210+gn bullets... you still see the 30" barrels, even with 10-11 twist, as the dominant length. Some people may use 28", some may use 32-34", but the vast majority are 30". Its about the best compromise between 'free velocity' and still being able to find a case to transport the dang thing in