The 300wsm has better brass available. You can build a 7-300wsm easy to reload for and you have the good brass with the high bc 7mm bullets. The 7mm will have plenty of energy to harvest game out to the range you are talking about. I have had both I like the 7wsm a little better.
I always go with the larger caliber all else being equal. However I would gladly shoot the most accurate one and kill anything I wanted in Wyoming with it. In other words, personal prefference. I have two 300 wsm's and no 7mm wsm's but that doesn't mean I couldn't take the 7mm wsm and kill just as dead with it. Paul, down at wildcat bullets has been working with some very good high bc 7mm bullets for the 7mm wsm. I think that is one of his favorites to shoot. Can't argue with that choice. Which is better, 30-06 or 270? I would say if you do elk size critters get the 300 wsm. Anything smaller and it is a wash.