There are many areas here where you can see, and could
theoretically shoot, a lot farther -- both in sage desert and in the mountains in steep terrain.
My practice so far has led me to this set of guidelines:
Offhand, standing, 150 yards max with hasty sling.
Seated, 250 yards max with elbows supported.
Using shooting sticks, seated, 350 yards max (so far -- some refinement still left to do).
Those are the maximum distances where I can pop balloons. I did pop a couple standing offhand at 300 yards, but if I can't pop them ALL, I don't think I should hunt that way.
I MIGHT be able to pull off a 400 yard shot with sticks. I'm going to do some more field practice and see. Even from a solid machine rest, though, a good 3/4 MOA rifle would shoot no better than 3" groups in dead-still air.
I figure 400 is right about where a .30-06 really starts to tail off, even with good polymer-tipped bullets, good loads, etc. If I don't plan to shoot any farther, it should hold its own. In the real world, with wind, imperfect rests, adrenaline, etc., I really don't think that I could call anything past 400 an ethical shot, at least for me. Probably closer to 300, and not just a quick offhand shot, either.
I figure I should practice FARTHER away than I would shoot while hunting, not just practice at 100 yards and pray that my rifle and I will hit something at 4 times that distance when the chips are down.
The 7mm Rem Mag's numbers do look pretty good. If I didn't already have a rifle...
So, I'm sort of back to my original thought -- a serious elk rifle like a .338 or even a tad bigger, and a crazy flat shooter like a .257 Wby for antelope and the like, might be worth adding, with the .30-06 to fill in the middle of the spectrum, act as a backup rifle, etc.
Thanks!