Goodness sakes. A 30-06 is a deer rifle? I'd hunt anything in NA including the Big Bears with one and so would the majority of all the people with equal or greater experience to yours. What is a 180gr Partition or TSX going to do better at 3000fps that it won't do at 2800fps inside of 400yds.
If you would like to argue that point, I'll just bow out and let people like Finn Aargard and Phil Shoemaker do the talking for me.
Or maybe my Uncle Dempsey who used a Featherweight .308 from the 60's til now to shoot every big game animal in Canada. Guy has over 300 animals on that gun and most where from Northern BC and the Yukon.
AH yes but you neglected to include all of what I said in your retort, "6-700 mtrs is doable with a 300 mag". Anyway I just opined my experience. I did not limit my ranges to 400 yds as you did and THAT my friend is where the difference comes in between the '06 and the various 300 mags. The OP expressed interest to 1000 mtrs, I answered his question as expressed.
You have obviously never hunted the big bears, so it's easy to say you'd do it with an '06. I on the other hand have, and feel a 375 is barely adequate, and feel more comfortable with a 416. Hunting and shooting the big bears with everything on your side and the bear not knowing you're there is one thing and can readily be done with an'06. It's when things change and the wind whips around and all of a sudden it's no longer on your terms and you're looking at 12-1500 lbs of really pissed bear who just discovered he's not alone and really don't like your smell or the fact that you're within 200 mtrs of him, that even a 375 don't give you a warm and fuzzy feeling inside and an '06 makes you feel like you're holding a 222.
May I suggest you spend some time around and hunting the big bears before you opine the 30-06 is adequate for them!!! The Alaskan outfitters and guides who hunt the big bears almost to a man carry .375s and larger and I know 3 who use 458 WM for back-up on the big boys. 416s are also very popular and have a much better range for those "he's getting away" shots.
So all I have to say to those of you who would hunt game well beyond the capabilities of the 30-06 is make sure you go with a good outfitter and his guides carry a rifle suited to the big boys, 'cause you're NOT !!!!