I believe Bevan King makes a 9.3 barrel, and Bits of Pieces in Vancouvers sells Heym barrels in 9.3mm.
One other option is to build a .358 Norma - it offers good performance and ther are many options for bullets. From light pistol bullets for plinking all the way to 310gr heavyweights. Brass is easy to make from cheap, readily available .338 Win Mag. stuff.
And for the original question, I like all of the choices. The 9.3 has a tremendous amount of performance while burning relatively small amounts of powder. You can easily fit 5 rounds in a magazine and the relatively mild recoil means a lightweight rifle is still manageable.
BTW, I tried to find some .375 Ruger brass recently (and dies) and it wasn't an easy task. GH - only your father had some in stock. I should have called him first, but I tried to get it locally first. I called every local shop and got the same answer- no dies, no brass, I can get the dies, I don't know when I can get the brass. The only good thing that came out of the search was that I started doing business with your father.