Interesting thread. I've been looking long and hard at building a heavy .243, standard not improved, with a 1:8 twist for shooting 105 grain or heavier bullets. I'm getting just over 3100 fps with Reloder 22 but my standard barrel doesn't want to stabilize those long bullets.
The other posters are correct, if you want to shoot long distance, good mounts and glass will be just as important as the rifle. Don't skimp there or you'll be disappointed in the result.