I've used a number of Bartlein .308 barrels with 0.299" and more recently, 0.300" bore diameter. Frankly, if there is a difference due to .001" bore diameter variance, I think it is largely overshadowed by other normal barrel-to-barrel variance. I recall hearing somewhere that the origin of the Palma 0.298" bore had something to do with slightly undersized (diameter) bullets that were provided to competitors at some point in the past, but I don't recall exactly where I heard that.
As far as freebore, the neck length of a .308 case (SAAMI) is approximately 0.303". To keep the boattail/bearing surface between the neck/shoulder junction and halfway out the neck means you have about 0.150" freebore length "adjustment" for various bullets. That's really quite a bit of leeway. For those that use a no-turn neck chamber, donuts don't seem to be the issue with a .308 that they are in some other cartridges. In my hands, a .085" freebore is plenty for the vast majority of lead core bullets under 185 gr. With that freebore, I can just barely seat 185 Juggernauts with the boattail/bearing surface junction above the neck/shoulder junction. Accordingly, pressure at any given velocity is higher than it would be with a more generous freebore. Dave Kiff at PTG makes a reamer designed for the Juggernaut that cuts .168" freebore. IMO, that's really more than is absolutely necessary. I load 185 Hybrids, 210 JLKs, and the 200.20X bullet in a chamber with 0.180" freebore; they seem to work just fine. Some of the newer 200 gr offerings with exceptional BCs (200 Sierra MK, 200 Jack) have actually gone the other direction. A freebore in the .090" to .120" is sufficient due to the shorter bearing surfaces. For comparison, I've also loaded the 200.20X bullet in a rifle with just such a relatively short freebore and they work ok...at .010 off the lands they are seated pretty close to the neck/shoulder, but not below. The bottom line is that the information necessary to determine an optimal freebore range for a given bullet is usually available online or in various books such as Bryan Litz' "Ballistic Performance of Rifle Bullets". Clearly a single freebore length may not always be optimal over the entire wide range of .308 bullets currently available, but with about 0.150" neck length to play with, it shouldn't be too difficult to choose something that will work for a number of different bullet options.
For Berger's 155 offerings, the 155 Hybrid requires a little faster twist than does the Fullbore or VLD, but a 12-twist should be sufficient for all of them under most conditions. In the 185 weight class, an 11-twist will usually be sufficient. For the 200 gr class and up, you'll generally want a 10-twist or better, although myself and others here have all found an 11-twist to be sufficient for the Berger 200.20X and 210 JLK bullets, even if it is not fully "optimal". In terms of the monolithics, they are a whole different ball game. Because the sectional density is lower, they are much longer for a given weight class and therefore require much faster twist rates, typically around 9.5 to 9.0, or even faster. I would generally choose a twist rate based on the whatever was the fastest twist rate required amongst the various bullets I intended to shoot out of a particular rifle. For example, the 200 Jack bullet is long enough (~1.578") that even a 10-twist is theoretically not sufficient according to Berger's Twist Rate Calculator. I'd probably go with a 9.75- or 9.5-twist if I were going to order it directly from Bartlein. However, 9.0-twist barrels are often immediately available at online vendors. I recently ordered a couple barrels and didn't want to wait several months, and so I went with 9.0-twist barrels from Bugholes. The 200.20Xs and 200 Jacks seem to be working just fine with a slightly faster-than-necessary twist. As with bore/groove configurations and freebore lengths, I think you have enough play that there isn't any single "correct" answer. With twist rate, I'd rather it be sufficient for the longest bullet I intended to use, even if it meant spinning some other bullet a little faster than necessary. But that's just my personal preference. Regardless, even with the current availability of various competitive bullets, I think there is more than enough play in each of these parameters to set up a rifle capable of shooting several different bullets well. In other words, with a little planning it doesn't necessarily have to be optimized for one specific bullet to the exclusion of all others.
