Again as to the .300 Win Magnum choice.

I would personally go for the obsolete and now rare .300 H&H Magnum.

But that choice as a standard offering is called commercial suicide. The .300 Win Mag is no doubt asked for many times more than a .300 H&H Mag. I imagine getting a Highland Stalker Magnum in .300 H&H magnum would not be a big drama.

A slimmer barrel? Are they so much more expensive? No idea.