I really cannot see the point of shooting 320gr bullets from a 9.3x62 unless you are going after a wounded lion at 30yrds range, which no PH would allow. The 285/286gr loads are about ideal for the heavy stuff as they give longer range and better penetration than the 320/325gr. The 325gr Normas are designed for the standard 1:14 twist. There is a down side to a fast twist even if it is minor. More recoil more torque effect, more fouling, lower velocity, faster barrel wear.As I said very minor but if there is no improvement in bullet stability why not just accept the established gun manufacturers' norms.
This article from Real Guns may interest the handloaders. The Gun tested is a Ruger 77 with 23" barrel.

http://www.realguns.com/loads/93x62mm.htm