I'll admit I've been too busy with other aspects of my life for the past several weeks to answer many of the questions on the forum. Hopefully, it slows down soon and I can spend more time here. But with that said, for the times when someone doesn't get an answer in what they determine to be a reasonable period of time, and they can't find it in the FAQFAQ section, I'd suggest they try using the Search function of this forum. By putting in a few words pertaining to your question, you can usually find dozens of related posts made over the past years. The beauty of this forum is that there are lots of knowledgeable folks who have willingly shared their thoughts and suggestions on hundreds of topics. I won't say every topic has been covered. But when you consider that there have been over 37,000 posts made on nearly 5300 topics, chances are you'll find some useful information if you make a proper search. If you find the answer you're looking for, don't hesitate to post a follow-up, along with a link to the original post. If you still have questions, make another post that provides more information and asks specific questions.
Remember that we all have different styles, techniques, site / soil variations and different levels of physical capabilites (hearing, sweep speed etc). As such, there is no single definitive answer for target depth, coil size, coil design, Ground Phase numbers, Sensitivity settings, Volume levels, Noise Cancel channel or even Threshold settings. I don't talk a lot about the numerical value of my settings because I know that some can be mislead by trying to duplicate another's settings, without considering the differences mentioned above. I will say I usually max out my volume, run a positive ground phase, keep my sensitivity as hot as I can while minimizing a reflective transmit signal and hunt in multiple tones with minimal discrimination. And I don't talk much about the depth capabilites of specific coils because again, there are simply too many variables. I have found that, between those two coils, I have to lower the Sensitivity a couple clicks on the HF, compared to the MF, or it chatters. And if pressed for a "depth report", in my soil, the two 10.5 DD coils are comparible in depth, on coin sized targets. Quarters at 10 inches, small copper cents at 8 - 9 inches and dimes at 8 inches. But again, your results may vary.
The best advice I could give anyone who is unsure about detector setup or hardware preference would be.........Remember, at any site, your objective is to neutralize the effects of the "atmosphere" and soil, maximize the transmit signal into the targets you seek, and be able to clearly hear their return signal. ........learn what makes your X-TERRA work. Understand what each setting does and how one setting may impact another. Chose the coil that best accomplishes the task at hand, based on the differences that have been discussed on this forum many times. Most importantly, enjoy the hunt. JMHO HH Randy