For an evaluation of bullets ballistics see JBM Ballistics. http://www.jbmballistics.com/ballist...culators.shtml
For the stability numbers (twist rates) - http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Primary factors affecting twist rates / bullet stability are -
Bullet Length
Atmospheric Temperature
Altitude

Unless you use a very long (heavy) VLD bullet, near sea level, in very cold conditions, a 1 in 8 twist is OK and typically easier to get.
The early M-16's had a 1 in 14 twist until they tested them in the arctic.

However for my new Savage I decided to wait the extra time for a 1 in 7 twist, since I may use it for 600 and 1000 yard shooting. For me the faster twist was cheap insurance, but your needs are probably different.

Mike L in TX