Sounds good! I'd not use 300's unless I was deer shooting only and would normally go for the heavier 405gr. right off the bat. For 405gr. RP load performance, check with 9.3x57. He's done some steer head testing with it and it's peformance was MOST surprising, especially when compared with the 300gr. Swift results from his .375H&H.

In that DR, you can actually drive the 405gr. RP's, using handloads, to an easily accomplished 1,800fps with safe loads. Experimentation with handloads and how they shoot, is up to you.