I know you like to quote that 2900 fps number Luke, but I've messed with 30-06 loads quite a bit. Been shooting and loading that round for years and pushed the limits a number of times. I believe that number IS possible, but only with very specific combinations of bullets, powder, and barrels. I'm positive it also involves loading over SAAMI pressure spec. If you want to push the number out to include those statistically rare examples, I'm sure there are plenty of people getting faster than 3050 from a WSM as well. Just don't want people thinking they can pour the powder to the old '06 until they hit magnum speeds just because Luke did it once. May work... or it may not.
Now that I have said that... I do agree that a carefully tailored handload makes the gap between a '06 and regular factory .300 WM pretty small. One reason why I use a '06 for the majority of my hunting, up too and including grizzly.
Ok, back to the original question. In your shoes I would just use the 7 mag (assuming its a mag?) and 160+ gr bullets for everything, but if you want another Tikka I'd pick the .300 WM over the WSM. No difference in the guns, and a .300 WM will have a better selection of loads and slightly more performance upside. Field difference would be near zero though.