Gunnar, thus far in my soil PP or all metal don't appear to be any deeper than discrimination, but I need to test further, but then again I'm so impressed with the depth of the GT with the stock 10" coil and especially with the 12x10 that I don't see any need to hunt in PP or all metal. Thus far every time I test them against each other discriminate seems deeper. In fact, I don't like to use PP mode to PP because often it won't even hear a deep coin that discrimination easily nails. This is in my somewhat mineralized soil, of course, which ranges from low to high depending on site. I've owned just about them all but this thing is the deepest yet. Also, machines with higher than about 8Khz (signal frequency machines that is) never ran smooth or got the depth in my soil. So it depends on what type of soil you have that you consider bad. Different "bad" soils can be of very different types than other "bad" ones, where a machine will do very well. For instance, I recently read of one guy who has some rather bad red soil, and he said of all his machines (one or two flagship models) the GT when ran slow will even null out a lot too in his rough ground, but darn if it's not popping him deeper targets than he ever saw before. Read many examples of this and have experienced it myself (owned most of whats out there). I think the BBS frequencies biased in the lower range in some respects below say 12khz (since they only range up to 25khz) are punching through my minerals like no other, and is the reason they get the depth and run as smooth for me on my mineralized beaches and land sites.
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...
