I'm not too familiar with the ballistics of the 356 or 358 Win, but I do own a 375 H&H (bolt action) and a 45-70 double. In fact, I had a 458 Lott in Ruger #1, but sold it. So I am familiar with big bores (though the 45-70 may be a bit light). It's just the 375 Win really looks compact, but from what I'm hearing it sounds to be more like a 338 Win mag or even the 300 win mag in performance. Just not large enough for a clean ethical kill on something like a cape buff.
What is so attractive about this gun is that it's a lever action, so it can hold several shells, it's quite accurate and has quick follow-up, second only to a semi-auto. A lot of pluses in my book.