The 10" Tornado is the best stock DD coil I've ever used on any machine. Much better than the various old 10" Explorer coils IMO. It's got good separation, excellent depth, and is very stable. In fact, I've thus far dug my two deepest coins with it at about 11" deep. I have yet to dig coins that deep with the 12x10 but my tests show it is deeper. In one test at a sensitivity setting of 3PM the stock 10" coil coil not even see a dime I buried but the 12x10 did without touching the sensitivity. The Tornado made it's appearance with the introduction of the Elite and continues to be made to this day. They have also replaced the heavy BBS coils on the Xcals as well.
A few more bits...The 12x10 is more stabile, allows higher sensitivity settings, and is a nice improvement in coverage you can really notice. It's also got better separation and seems to make tones more crisp. The odd thing is the machine feels sped up because of it's laser like detection field too. Detech and Kellyco claim the SEF coils are a hybrid of concentric and DD coil fields for the best of both worlds. Some believe that and say there is a small concentric-like center to the coil roughly the size of a large soup can. I used to think that but am not so sure, as the DD line seems very sharp from tip to tail, but is even sharper near the tip and tail. Either way, whether it's a concentric/DD hybrid or not, it is for sure a very unique coil with a unique detection field, and if it is partly concentric I'd say 90% of the field is DD...But a VERY sharp DD that makes for outstanding separation, and also since it's a less "fuzzy" field it rides on and sees less ground stew which equals more stability and higher sensitivity levels without the target being washed out by the ground matrix IMO. Use the tip to really sniff at stuff you think might be severly masked, but even the center does a much sharper job than any DD coil I've ever used at separation, big OR small IMO.
Here's a few pics of the 10" Tornado and 12x10 for size comparison. You can search on your own for various threads from others and me that compare both coils. One of which in which I go into detail on depth comparisons on buried targets with the two. For that reason I believe the 12x10 is a deeper coil even though my Tornado thus far holds the record at 11" for two coins, but I honestly haven't used the 12x10 at known deep coin spots yet to see if I can beat that. For one thing though, I am popping wheats and silver dimes in dry conditions at depth much more frequently with the 12x10 than I ever did with the Tornado at those same sites under dry conditions. That, combined with the fact that in one test the 12x10 could hear a buried silver dime at a 3Pm sensitivity setting but the Tornado could not, lead me to believe the 12x10 is deeper. It also seems more sensitive to tiny targets and seems to hit coins on edge even better than that already excellent ability of the Tornado. Not knocking the Tornado. Great coil. Best I ever used. It's just the 12x10 raises the bar even more in all performance aspects IMO.
Here's one link to a long in depth thread I wrote on the impressions of this coil, as well as to the 10" Tornado. Search on your own for "12x10, Tornado" (ALL WORDS, ANY DATE) and you'll find a ton of threads in this forum on them compared from people and me.
http://www.findmall.com/read.php?21,1293994,1294614#msg-1294614