In terms of the POI being low, it just may need a slightly brisker load. I've played extensively with four doubles - two act as expected and shoot apart at lower velocities, come together and then cross at higher velocities. The other two will shoot the correct weight bullet together at a range of velocities (+/- 100fps) but with about a 6" variation at 50 yds in elevation - faster = higher. Calibres are 375H&H and 470. Maybe try some of those premium loads which give higher velocity at normal or lower pressures. they are currently being discussed in the big bore rifle section.

BTW - if I was planning a DG trip and was not a handloader I'd buy a rifle in 458 rather than 470 because for a given amount of money you can have so much more practice with a 458 because of the lower cost and I reckon this would more than make up for any possible risk of failed extraction.

mike