A 300 WM will not handle light bullets or reduced loads as well as a 30-06.

I use both cartridges and find that where a 300 WM shines is with heavier bullets. I often use bullets that weigh between 150 and 180 grains in a 30-06 but in the 300 WM it is always either a 180 and 200 grain bullet for me. The heavier bullets are very useful for thumping larger game (elk and larger). The 300 WM offers a little more range than a 30-06 but I doubt if you will get much benefit from that in a factory rifle with a light weight barrel. For practical purposes I doubt if you will gain more than 75 yards in real world situations, but you will certainly gain some recoil

The Tikka is not my cup of tea but most guys that own them are very happy with them. They seem to be good solid hunting rifles, as is the Ruger. I like the factory trigger on the Tikka much better than the factory trigger on the Ruger, but of course the Ruger trigger can be improved significantly either by a gunsmith or with an aftermarket trigger. Neither rifle is a perfect choice for a true long range rig, but both are fine hunting rifles.