In my opinion, and we all know how much opinion's are worth, I don't see any appreciable difference in the depth detection between any of the three models of X-Terras. Not when all of them are equipped with the stock coil and properly adjusted for the site. However, there are many differences that allow me to better adjust my detector to the soil and type of detecting I do. For example, I prefer the X-70 as it allows me to "fine tune the settings" specifically for the site and soil conditions. Although I believe, for example, the maximum and minimum sensitivity settings are the same for all models, I like being able to select from the 30 possibilities on the X-70 compared to having 10 on the X-30 or even 20 on th eX-50. I also like the X-70 because I've found that I "hear more" when I hunt in a multiple tone mode. Four tones is good. But I like the 28 tones better. The X-70 allows me to run with a slightly audible threshold. When hunting with a rejected notch segment, that threshold tone blanks when sweeping over a rejected target. For those wanting the simplicity of "auto settings", it offers Auto GB, Auto NC, Tracking, Beach mode etc. And even though I can set the GB automatically, the X-70 allows me to implement a manual override, so I can run a bit positive. Although I am not a nugget hunter, the Prospecting mode offers a true "all metal mode" with adjustible iron mask capabilities. I use the Prospecting mode for target sizing and determining the general shape of an "iffy" target. As someone who primarily hunts for old coins at old sites, I really like the target response and audio provided by the 3 kHz coils. In my opinion, deep iron is much more easily distinquished when running in all metal, multiple tones, with the 3 kHz coil.
If you are a land hunter, and don't plan to prospect with your detector, either one will do fine. But if you have the funds to go with the X-70, the reasons I gave might give you some additional thoughts prior to making your purchase. Bottom line, you won't go wrong with either. Thanks for the interest. HH Randy