I would agree, if your thinking about elk out to 1000 yards, a 300 RUM is the min I would recommend and a good 338 would be even better on these heavy critters at these ranges.
A 338 RUM, 338 Edge or 338 Lapua would all work very well and offer you all the performance you will need for this range and in easy to load for rifles.
If money is not an option, I would certainly go with a top end custom receiver, McMillan A-5 stock, quality barrel, 28 to 30" range of at least #7 contour. Fluted if weight is a concern. This will not be a light rifle but a 1000 yard rifle needs to be designed for that purpose.
These rounds are more then needed for blacktails at these ranges but dead is dead. That is never a bad thing. Undergunned is the real sin here and if your hunting elk, better to go bigger then smaller. With the new muzzle brakes
we use today, recoil is not an issue with anything you use.