Out to 400 yards a 160 gr 7 mag bullet and a 180 gr 300 bullet are almost identical in trajectory, with the 300 having a slight edge in energy. At around the 400 yard mark the energy evens up and at any range longer than 400 yards the 7 mag shoots flatter, has more energy, and less recoil because of the more aerodynamic bullets. On paper I have to give the edge to the 7 mag. But I'd choose the 300 WSM if I wanted a magnum. Hard to explain exactly why, I just like it better. Sometimes you just throw out logic.
I haven't run the numbers, but a 200 gr bullet from a 300 will beat the 7's in energy at any range and be pretty close in trajectory. This is where the .30's are the most aerodynamic. At extreme ranges you need a good range finder and if you know how, you can always compensate for a little more drop.
I've had 'em all. I won't be shooting beyond 400 yards, so a 30-06 with good handloads would work just fine for me. If it were me, I'd keep things simple and either add another quality bolt rifle in 30-06 or trade the pump for one. If you are looking for a 600 yard elk gun you need to be honest with yourself. Are you really good enough to shoot that far? A properly loaded 30-06 will do at 500 yards exactly the same as the magnums will do at 600. And with a lot less expense and recoil.