Personally, I have tried many of these settings, but never really seen any real improvements on the ground I'm working. I have found that I have gotten better depth overall when I run a lower "sensitivity" and stay out of Difficult soil condition. I prefer to listen for the faint whispers or disturbances in the threshold than listen to all the extra background noise running some of the extreme settings. I guess it comes down to a persons personal preference. I have always ran the SD, GP and GPX units lower and concentrated on faint signals and had good success. Over the years I found some really nice deep nuggets.
I have tried running "Semi Auto" Ground balance and found it very difficult to stay ground balanced where I hunt. I have used this setting with and without the Ferrite ring trying to get a good balance, but have much better results Auto Balancing with the Ferrite.
Just my thoughts.