Hey Denny,
The machine performed flawless at DIV even with the extreme conditions. I saw many other detectors fail the first day but everyone I spoke to that used the F75 had no problems at all. I use the all metal mode 95% of the time and it's awesome. Even in iron rich campsites, hell the VDI readings it gives in all metal have been right just about every time. Dig anything that gives you a reading of 15 or higher, I have dug cuff buttons that have read at 15 on the VDI. When conditions don't allow for the all metal mode (Trashy sites) I do use the discriminate mode, it has worked well too. I use the DE mode, Discrimination set at 7, 3 tones, I like the three tones because the Fisher CZ series used three tones and my old ears got accustomed to them. Start off high on the sensitivity and work it down until the chatter is almost null. The most important thing (IMHO) is to ground balance often, in both good and bad ground, I use the fast grab option to GB and have checked its setting's against the manual GB and it's dead on, once the machine is GB you may want to manually set the GB up a couple of notches to help with ground falsing.
There also is debate on this forum as to whether all metal will actually get you more depth than the discriminate mode, from my own personal observations, I believe the all metal will "see" deeper.
Hope this is some help to you, I am sure there are about 100 or so varying opinions on how to use and set the machine up, this is what works best for me. Good luck with the machine and good luck digging. The sign up for DIV X will be sometime the first of April.