Having hunted in sites in the mid-west where there is clay, I have found it to be very mild and not a challenge to most detectors. The red clay that Daniel is referring to is that "crap" we deal with that starts in the eastern edge of Alabama, goes into northern Georgia and is in some areas of North & South Carolina and then the central areas of Virginia. So simply saying one hunted in red clay means little unless it is hot which most clay is not.
The area I tried the Deus at was near Kennesaw and for those that know the area, there is an area off 41 just west of Towne Center Mall that is well known for the bad ground there. Many detectors can't hit a Minnie Ball more than a few inches as you head up the hillside whcih is why PI detectors tend to dominate these areas. The Deus worked as well or better than other non-PI detectors I have used here in the past. The 12kHz frequency seemed to offer the best performance but the 18 kHz did give me sensitivity to lead and brass that turned up some percussion caps (size of .22 short casings) and buck-n-balls (fishing sinker size lead balls) down at 4" to 5".
I did get 2 bullets here one fairly shallow on the edge of the roadway (5") which target ID's correctly and was a clear "dig me" signal". The other was 15' away in the edge of the trees and bounced around . . . . fluctuating between ferrous and non-ferrous on the main screen icon with 25% black showing. The all metal non motion audio disc mode showed a more non-ferrous than ferrous signal and it turned out to be a 9" .58 caliber minnie ball. I did get some iron items but the signals tended to remain in the ferrous side of the indication . . . . . . I am planning to go back in a week or so and do some more testing in this and other areas around Atlanta that have hot, red clay conditions.
There was another spot I tried it at closer to the Mountain on some land I have access to and it is also quite hot . . . . well known for that as well in the area . . . . . let's just say it is "muddy" for those in the area that want to gauge to measure against. An hour there turned up 3 bullets - all 8"+ - and as George said in another post, the response sounded good but the target ID was ferrous . . . . . I believe that based on the response from some nails in the area that also registered ferrous, that one could identify and ignore some iron by the inconsistent response and jumpy target ID on deep targets . . . . . if you are relic hunting, I tend to dig most targets anyway as you never know what might turn up . . . shall frags, cutlery, etc.
Let me know if this helps
Andy