I shoot heavy VLD's out of all my guns. A 6mmAI just beg's for the 105 (or even the 115) VLD, assuming you plan to do some longer range shooting. The 1/8 twist is the general favorite for this weight range.
Barrel length is a personal preference. A longer barrel will get you more velocity, but might not be the best option for a "hunting" gun. Your style of hunting will dictate what is best for you.