well i better get my 2 cents in haha
i personally shoot a 300 ultra but my uncle has a 300 wsm he loves and i got him to try and push heavy bullets out of it and it just didnt have the case capasity to power the big bullets out at speed.
i have a friend that shoots an old 300 wm in the old blued barrel sendero with more rounds down it then id like to think about. it shoots great and is a super accurate gun.
really it comes down to what your gonna want to do with it and if you need or just want the extra longer case. personal prefrence.
some shoot wsm some shoot wm i shoot ULTRA MAG