Many of the old timers did indeed carry six rounds with the hammer down between rounds. But the old SAA's had a much more pointed firing pin than the more modern ones and, while the hammer never went fully down it went far enough to be safe in anything like normal carry and use.
They also carried those guns with the sear (trigger) in the "safety" notch (yes, Colt called it that and instructions said to use it that way), and did so with no concern, let alone the hysteria that such an action would cause today. What has changed is that we are now, thanks in part to massive litigation where everyone sues everyone else, much more safety conscious than they were in those days. All told, that is probably to the good.*
Would I carry "six up" in a SAA today? Probably not. If I were expecting to be in a gunfight, I would carry six, but in my Model 19, or a high cap magazine in an M9 or a Glock.
* Sometimes our concern for safety reaches silliness. I once mentioned on one of these sites that belt links from aircraft wing guns dropped down a chute and fell to the ground. Incredibly, someone asked if that wasn't dangerous for people on the ground. I pointed out that the bombs dropping on them were just possibly more dangerous than falling links.
Jim