goldseeker, you say that in addition to gold nugget hunting, you also plan to take the GPX out to do coin hunting too? Just be aware, that ........ while you can certainly get a coin down to 1.5 ft. deep (much deeper than any coin/relic/jewelry machine can), yet you might go crazy availing yourself of that sensitivity.
Believe it or not, as much as it might seem "the more sensitive, and the deeper, the better", yet it's not always true. If you took the GPX out to the average urban park, thinking "I'm going to get the older coins that are deeper than the poor saps with coin machines are getting" you will be a sorry fellow indeed. I mean, while a nugget hunter does indeed want to hear every piece of birdshot, staple, etc... (because nuggets found in nature are rarely ever larger than grain-of-rice-sized), the average coin/relic/jewelry guy DOESN'T want to hear every birdshot and staple. Do you have any idea how much little flitty junk is in the ground, at the average park or school, for instance?
As far at out in the boondocks anywhere (like for cache hunting, for the legend you speak of), yes, you may be away from the junk of urban blighting. But it's still not meant to be a cache hunter either. Again, you will go crazy hearing every nail or paperclip along the trail. A better cache machine is a 2-box unit, that specifically DOESN'T hear anything smaller than a soda can.
And be aware too, that most such treasure legends (lost mines, and other such lore found in all the old dime-store treasure books) are usually .... well ....... just embellished legends. Easy to believe, because the human mind wants so hard "not to be left out", but when you scrutinize the stories, it's ...... well.... stories.