As a user of .600's 30 years ago, I would ask how mauch penetration do you need to reach the vitals of a bull elephant or buffalo? Not once did I see too little penetration. Always enough. Yes, others may and will out penetrate the .600 in some test mediums. The .577 will go deeper, but how deep do you need to go? From having used both I can tell you from the effect on animals that have the CNS or brain missed, the .600 will do what a .577, .470 or .416 and others won't do.
Yes the Heym is probably too light. 14 will work, 16 is better. I had a 13+ Churchill that was tough to handle, but easy to carry, 16- H&H was much easier to handle, but tiring to carry.