My shooting buddy recently completed his 300 RUM. We shot it at 665 yards with the Berger 230 hybrid. Velocity was around 2900fps out of a 29inch barrel with a medium charge of Retumbo. 3000+ fps is probably attainable out of the 30 inch pipes. Accuracy was unbelievable, the first 3 groups on the new build were all under 4 inches at 665 yards with a mild breeze. It hit like a freight train as well. Our silhouette target has a 6 inch center disc on hinges and it ripped the hinges off the main plate. It had withstood hundreds of hits by 308s, 260s, 300WMs over the years. So if you are looking to really stretch out past 1k I think the RUM would do it the best, granted the WM probably wouldn't have that much trouble either. Downsides, they burn a lot of powder, brass is tough to find, not a great selection of factory ammo, NEEDs a brake. I know my shooting buddy loved his WM before the RUM, but he definitely despised the belted case of the WM. My .02
JWV