I used 4X lacing with large flange hubs on my track bike when I competed. I tied and soldered the spokes for added strength. That was the only way I wouldn't break spokes. That was back in the 1960's when ss spoke technology was not very good.
8 years ago I laced up a set of 36H SF Campy hubs using 4X for a cross bike and have had no problems. I have ridden on a lot of dirt and haven't broken any spokes. The only problem is that the head-in spokes tend to rub across the head-out spoke ever so slightly. Some site that as a disadvantage but, so far I have had no problems. I think that it is a toss up between 3X or 4X lacing. It is a little easier on the pulling spokes as the spokes meet the hub at a better angle.
In any case, one needs to think about the loads on the wheels when touring a fully loaded bike and rider.