I've owned 35 Whelen and 338-06, let the 35 Whelen go. No first hand experience with he 9.3 but I do have a few observations.
I believe in some African countires they allow the 9.3 for hunting some larger game and not the 35 Whelen because of minimum caliber restrictions. I cannot see where it would make a bit of difference. Neither are big enough for me to hunt the big boys with but the 9.3 meets their requirements and not the 35 Whelen if that is a concern.
357 pistol bullets can be loaded light in a 35 Whelen for small game hunting. Not something I'm interested in, but an option for those who are.
All of these rounds are the poster boys for the anti-magnum crowd. But a 300 magnum loaded with well constructed 200-220 gr bullets will out penetrate any of them and do it with less recoil. There isn't an animal on the planet I'd hunt with either, and not hunt it with a properly loaded 30-06 or 300 magnum. If you NEED something bigger, you NEED to move on up to one of the 375 magnums. If you WANT to hunt with something a little different and still have an effective gun either will get the job done.