With the NEL Tornado coil, my ATgold ground balances at or around 69 on the ground in my test garden. Can run at max sens, with non-annoying slight chatter(less than say an f75), totally stable at -1 sens.
It weighs a little more than the 8.5x11, it's not too much more, and still feels very handy to swing, does carry a little more momentum at end of swings, feel very balanced though. Loaned my scale to friend to weigh a turkey yesterday...
here is pic of 8.5x11 and 12x13 tornado next to eachother
8.5x11 & 12x13 tornado
I'll just post the pic links of my air test results, not gonna have time to put results on a chart of any kind. Air tests in disc 1, -1 sens & All Metal at -1 sens
air tests w/items
air tests with ruler for reference
Garrett 8.5x11 DD, CZ21 10", NEL Hunter 12x8.5, Nel Tornado 12x13
This'll prolly be slightly confusing, but, my abbreviations for the pic: AM=all metal, CR=classring(the further CR's), GR=goldring(thicker female band), SR=silver ring, Plat or E/p=platinum horseshoe earing (no minelab except xtera705 w/18khz can see this one, f75/f70 with 5"coil can slightly see this earing, t2 slightly, CZ can't), CR/Cross=cross (14kt, no minelab can see it ctx/excal/etrac except xterra705 18khz, nor CZ's, F75&T2 can slightly), P=penny, 5=nickel, 10=dime, 25=quarter,
As far as my test garden, I have pennies/nickels/dimes/quarters, each at 4/6/8/10 inches and a nickel and quarter at 12 inches, all measured from dirt/ground level and buried 3 years ago. Right now the post winter grass is fairly weak/thin, so results could be less with thicker summer grass.
With the Tornado in disc 1, -1 sens, it gets every coin, the display # changes a couple times on the 8's, a few times on the 10's, and a few or more on the 12's, but get's them very well. In all metal, -1 sens, the display # is more stable and it would be hard to miss any of the targets, even the 12's, it will signal the 12" nickel a few inches above the ground at max sens without having to be "right on it" (chatter at max is less than an f75).
The 8.5x11 is a great coil, in all metal it really gets down there too. The Tornado does even better, nothing drastic, like .5 to 2 inches deeper, but does cover a nice big swath with each swing. The 8.5x11 garrett coil did better than the Hunter all around.
Typed this fast, so don't quote me