Neil, not all my sites are mineralized. Here in Northeast Ohio we have soil that ranges from rich deep dark top soil all the way to hard packed limestone based clay. We have a lot of limestone bed rock in my area. Many of my sites are mineralized, though. Not all, but many. The Sovereign runs smoother over these sites than any machine I've ever owned.
I've seen references to that same fact from other people here and there. For instance, I think his name is JBow. I remember a message from him where I think (from memory!) he said he used an Etrac and one or two other flagship detectors at one particular site. None of them would give steady target IDs and were having trouble with the soil. He said he fired up his GT and it was giving him much more stable target IDs and he made some good finds there with it.
Why is that? Why would those flagship models have such a hard time with a particular site while the GT did better? You tell me because I'd like to know. Is it the frequencies being put out on one machine versus the other? I don't know. All I can say is that I had a much harder time keeping my Explorers stable at some of my sites than I do with the GT. I think my soil "likes" BBS better, but that's just a total guess. Take it or leave it.
I'm sure Minelab has a very good reason for using such high frequencies on FBS machines. Obviously there's some kind of reason or they wouldn't need to do it. I just would like to know what that reason is, and whether (it appears, anyway) those high frequencies can cause problems in certain mineralized forms of ground matrix. Maybe it's not a common thing and some of the sites I hunt are just the "perfect storm" in terms of minerals that can give it problems.
Think I'm finally home after a lot of years searching for my particular needs. Custom 1.5 lb lighter 
Sovereign GT (easy to do by just "building" lighter shaft) & SEF 12x10 as everyday coil. 8" Tornado (actually 7.25") as super heavy trash coil (Very deep & separates better than typical 8/9" true size coils). 13" Ultimate for large fields/beaches on certain days I want to grid faster than even the 12x10's nice improvement over stock for that. Stock 10" Tornado stays on water rig (stock shaft). 
ProPointer. Owned 15x12 & SunRay S-5 (5.5") at one time. Loaned a prior 13" Ultimate & SunRay S-12 (12.5").
Some Oldest Silver- 1835 Bust Dime, 1842 "O" Seated Dime, 1855 Seated Quarter, 1858 3 Cent Piece, 1891 Seated Dime, & another Seated Quarter too damaged to read date. Highest Value- 3 Cent Piece, Seated Quarter, & now 1921 F-12 Standing Liberty. Oldest Coin? Got to give large cents a good look & see. 2013 so far- 1 Seated Quarter, 1 Barber Quarter, 1 Standing Liberty, 2 Washingtons, 1 Barber Dime, 9 Mercs, 3 Rosies. 1 War Nickel. 19 silvers in total, & 1 1872 key date Indian, 2 Bufallos, 1 man's 14K gold medium sized ring & 1 gold chain, with possibility of few 8"+ deep mystery coins being Indians after cleaning.
What matters in life is the journey and not the desitination. How you handle that journey determines if you were a success, not so much what you achieved if and when you finally get there, especially if you made it by stepping on people along the way...
In loving memory of my long haired (wooly) husky Sky. She taught me just how beautiful and pure a soul can be, human or not...
