Having a barrel cut with a specific twist for a specific bullet is a science. If you want a barrel that will shoot more than one bullet and bullet weight then you have to compromise.
My general recommendations for the two cartridges mentioned are: 1:12 is too slow, 1:8 is too fast. 1:9 or 1:9.5 is about right, unless you will use mainly lighter bullets, then 1:10. Remember, a bullet is at it's most accurate when it is "just stable" at the muzzle. This is usually considered to be a Stability Factor (SF) of 1.3-1.5.
A 1:8 would be appropriate for an extremely optimized and heavy VLD. A 1:12 won't stabilize some heavier 7mm bullets at moderate velocities.
The Hornady 162gr A-Max is a very long bullet for its weight and diameter. As such, you will need a 9 twist or faster to stabilize it. According to Hornady, my 10 twist Hart barrel (7STW) will only keep this bullet stable for about 100yds before it becomes UNstable in flight.
I'd opt for the 9 twist which should be capable of handling most bullets up to 175gr. An 8 twist barrel may be good for a particularly long and heavy, special purpose bullet but I really don't see the practical use of it.