There's also a considerable difference when shooting at higher elevations. A general rule is that every 5000 feet in altitude requires 1" less twist for bullets to stabilize.
20+ years ago I had a 6.5-06 with a 1-9 twist, because a barrel company offered to build me one--and that was the fastest 6.5 twist they offered at the time. Generally I hunt locally at around 6000 feet above sea level, and the rifle grouped 140-grain Berger VLDs into 3" for 3-shot groups at 600 yards. Obviously they stabilized very well.
The Berger bullets stabilization formula (and some others) can provide a good comparison between various altitudes, and other programs work well too.
