I have owned two 9.3x74R doubles - A chapuis and a Merkel and my vote is for the 9.3x74R over the .30/06 anyday. I am not saying the .30/06 isn't a great cartridge, but in a double the 9.3 is a far better choice and will kill almost anything that walks this planet.

The issue of extraction has already been covered but I don't think anyone has mentioned loading the double. When you drop two large rimmed rounds into an open double rifle, they just slide home with a satisfying "thunk" and then you close the action and you are in business.

With rimless rounds, like the .30/06, you have to push them home, over the extractor, which takes a fraction of a second longer and is one more area where a failure, malfunction or simply not pushing them all the way home, can cause a problem. Double rifles were originally designed for rimmed cases, it is as simple as that.