Here is my opinion, and have never hunted leopard. So take it with a grain of salt.
I like the 300 H&H, but not Ruger No 1's.
I have zero experience with the 308, but prefer bolt actions, and have lots of 700 experience.
With that being said, I would use the 308. Comfort with the bolt action trumps IMO.
As far as the 150gr Interlock, I see no reason not to use it. My personal preference would be a 165gr, but I am sure I could kill a leopard with the the 150gr.
