Ironworker,
The difference between a 1x9" and a 1x8.5" is virtually (and may be, literally) non-existent, depending on the method of manufacture. It's not at all uncommon for buttoned barrels to vary by a half inch either way, so that 9" twist could very well be an 8.5" in reality, or even a 9.5". Cut rifled barrels tend to be a good bit more consistent in this regard, but both methods can produce good barrels, and I'm not knockign the buttoned variety. My point is, given a minor difference like this, I'd tend to go with the faster. A bit of extra spin will very rarely cause you any problem, while not enough will be a major pain in the arse every time.
Kevin Thomas
Lapua USA