bigwhoop,
with respect to your initial question, I have no experience with Merkel DRs.
However, I've owned 2 Krieghoffs, both 500NE 3" and used them successfully on elephant. I believe DRs are intended for close work on very large DG, so I would not use one in 375H&H. IME the 375 is a great cartridge - which will work on large DG - but better suited to a bolt rifle, IMO, where its accuracy, range and power are most advantageously exploited.
I am a very big fan of DRs, but would only consider one chambered for the traditional large bores designed for DRs such as the 450NE 3 1/4", 470NE, 500NE 3". YMMV
