civilian self defense ranges, ie, 6 ft and less, and with some practice, to 10 ft or so, as long as torsos are fully exposed. Doubling your chances of stopping an attack is definitely worth looking into. If it turned out to be longer range, you could just drop one gun (if it's DAO) or holster it, (just inside the pants, if need be) if it was an SA autoloader. Man, at 12 hits per second, and 800 ft lbs per hit, with 3 wound tracks caused by each hit, the 460 Rowland, 70 grs at 2300 fps, would really wreck your day.
In half a second, you could lay just as much shock and destruction on a ;guy as you could with a pump 12 ga and magnum buckshot loads.
.17 second splits are not that hard to achieve with a good SA auto, using loads that recoil like .45 ball. One in each hand means 12 hits per second.