Shoot like lightning but just a tad slow to load.
That's why you carry four. Two in your holsters, and two on the saddlehorn... :)
S'truth, the Confederates did that. The saddles they rode were an odd looking combination of the English flat saddle and the Mexidan/Western saddle. No saddle horn, but they had a sort of gun belt across the pommel that would hold two pistols.The rider would carry two in cross draw holsters, and some carried another one or two in shoulder holsters. Mind you, all these pistols could easily be of a different make, model, and caliber. Once loaded up, though, you'd be hell on wheels for a good long while.