treasure-salvor, you don't say the type targets you are looking for. Eg.: individual coins and jewelry ? Relics? Caches? nuggets? etc... But based on your mention of having a two-box type already, I'm going to guess your goal is caches, right ? Ie.: jar and box sized items, right?
If so, stick with the 2-box. NOT a TDI or Sov's with 15" coils, or various nugget setups. Sure they might go as deep, OR EVEN DEEPER. The reason you want to stick with a 2-box unit, is that all the other machines listed, will have the annoying side-effect of hearing every other items as well. Ie.: all the small target (coins, tabs, nails, etc...) will sound off. Thus requiring you to spend all day and night trying to second-guess large versus small. Instead, just use the 2-box unit, which won't pick up any object smaller than a soda can.
The depths on a 2-box, versus there other machines you list, on a soda or toaster sized object, will be about the same. But even if it's true that some other sort of coin or nugget or pulse machine went deeper on same-target, I'd still stick with the 2-box. For the very reason mentioned. That is, if your sole desire is for the big items , and you don't wish to fiddle with scores of little junk to weed through.
but if you're still un-convinced, and want depth at whatever cost, then sure: Go get yourself one of those super-powered minelab nugget pulse machines. Then take it out to ruins to detect at. Let us know how you do. I think you will *quickly* change your mind, and realize that "balls-to-the-walls" sensitivity is not always the best goal, for cache hunting.
