For factory load levels, I'd look closely at Speer and Remington 400 and 405gr. bullets. When driven at today's factory speeds, the Speer becomes a stiff bullet of the 2, yet the Remington will show penetration on ballistic media similar to a .375H&H with 300gr. Swifts. All at 1,320fps. See 9.3x57's Steer Head tests.

Interestingly enough, those ballistics worked 130 years ago and they'll work today.