The Sauer 404 is the one rifle I would trade a couple of my tried and true, well proven rifles to own instead. It is a wonderful design. I prefer the wood stock version, but that's an unimportant detail and personal preference.
I think the 9.3x62 is the perfect pairing to your big bore double rifle - use it for "everything else". Never have to worry about its effectiveness. Please disregard the marketing hype currently fashionable about long range shooting. Using a 9.3 is no range handicap for 90% of "real" North American or African game hunting situations. And the 9.3x62 bridges the gap between dangerous game and medium game without any flaws in its design or application.
The .243 is in another category. I have owned .243's and found them useful, but don't own one now. I prefer smaller cartridges like the .222 for small, furred or edible game. Less pelt and meat destruction with a .22 caliber centerfire. And I prefer larger cartridges like the 7mm08 7x57 or .308 for deer sized game. But the .243 would be a wonderful addition to a 9.3x62. Light recoil, flat shooting, and capable of taking smallish game with efficiency. Good for any time the 9,3 would seem too big or slow and so it fills a "gap" in your arsenal.
Sauer makes only high quality firearms. The 404 is their top of the line. You can buy a Sauer 404 and be assured it will work as advertised, every time, from the first time you take it out of the box. I have one of their older models, a 202. Extremely well made, accurate, and basically flawless. The 404 is just a little bit better.