Ultra long range means, to me, beyond 1500 pushing 3000 yds. I suppose that this would be at rocks and stuff.
I decided to go with the 375 Allen Mag on the large Bat action. It should be along, shortly. (I hope, I hope, I hope) Its my 67th birthday gift from me to me.
With current major factory bullet offerings (Sierra) as stated above, the 300 SMK and 350 SMKs are twins from the 338 and 375 cals.
However, Just a bit more development on a heavier 375 is what made the decision easy for me. Plus, Paul @ Wildcat bullets has a bit of twinkle in his eye about a 375 offering. Paul is really good to work with and will soon become a bullet maker to recon with.