Re: 300 WBY
If I had to choose between those 2 I would go Hart. I prefer Lilja though.
As far as caliber...what are you planning to do with it??
Either the 300 wby or RUM are fine calibers, just depends on how much "punch" you want. The 300 wby barrel life is longer, 300 RUM hits harder.
Yes a smith can make your new barrel have as much or little freebore you wish.
Long range shooting is a process that ends with a result. Once you start to focus on the result (where the shot goes, how big the group is, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.