In alll honesty you already have two that will work nicely. The 350 remington with some A Squares or Woodleighs would work nicely out to 300 yds easy. The 45-70 with some Cor Bon, Buffalo Bore or Ultramax loads in the 400 gr range would be some potent medicine. But if your stuck on wanting a new gun I'd have to say either of the 375's would be a good choice. One guy mentioned the 35 Whelen but with a 350 Rem that point is moot.