This is actually a rather interesting, and more complex than you might think, comparison. The simple part is that I have never found a situation where the Leicas pull a range but the Sigs do not. The first part of the complexity is that the Sig has a lot of different ranging modes (first, last, best, fog, battery saver (actually haven't tried this), and XR). The second part is that the Sig's beam divergence, 1.2 mils x .06 mils is super tight one direction but actually a bit looser than the Leica in the other. The Sig's beam is therefore not really any better than the Leica at picking up small targets relatively close. However, you can compensate for this by picking a different mode, like first, to favor the target, over the background berm or tree line. Furthermore, at least theoretically, the super tight verticle component of the Sig's beam allows you to get ranges quite well off of hill sides. In most situations you can therefore simply range the feet of the animal or where the post hanging a target meets the ground to range a small plate. Because of what effectively are a few more choices, the comparison becomes more complex depending on how long the user is willing to spend changing settings and strategies.
In practice, I haven't found a whole lot of difference in what the two will range out to about 1k. Out to that point, both will range either pretty much any target or the ground at the feet of pretty much any target. From the standpoint of hunting therefore, the ranging performance of the two really isn't much different. Both should range anything that is within an ethical range to shoot at. At around the 1k range though, the Leica's will start to encounter some things they have difficulty with. An example could be a target that is small and on a gently sloping pitch. The Leica could have trouble ranging both the target and the ground it's standing on in this instance. The Sig will range both the target itself further as well as the gentle hillside it's on further. A couple direct comparisons are that the Leica ranged a rotund human out to 1,228 yds whereas the Sig was still getting readings on the same person out to the point at which the path disappeared behind trees at 1440yds. It was doing this easily and would have gone further. Ranging tree lines, the Leica topped out at 1,850 yds whereas the Sig went 3,691. With hard targets the Leica basically won't go beyond 3k for anything wheras I have had the Sig to almost 10k. I think the best rules of thumb might be something like, with large soft targets like tree lines or hillsides, the Sig doubles the Leicas range. With large hard targets like buildings, the Sig triples the Leica's range. With small targets, the difference is less, perhaps 1.5x the range, depending on how well you tweak the modes on the Sig.
