Like I said, I only use PIs so I dont know how well Excals work, just seen others doing well with them, and yes most seem to just use either the 8 or 10" coils. Some use the WOT, and do good. Maybe there is a certain depth that is a cutoff depth on excals. I do know with a PI, it will go deeper and deeper with the bigger the coil, but the bigger you go, you start to lose the tiny stuff. I know my PI with a 9.5" coil will go 3' at least on bigger stuff like an anchor or chain, rusty hunk of iron, or metal bucket-unfortunatly. It will go 2' or more on a silver dollar, or a set of keys-unfortunatly. I also have a big PI that has a 5' x 3' coil and it will go 6' or so on a beer can, and pickup a car through the air at 25' or so, and powerlines EMI way off. But it wont find a coin the size of a quarter. Like I said, excals go as deep as they need, and skip the iron. For what I need for underwater stuff, a PI is fine for me. But a beach MD, would have to go to an Excal as the top choice. I think they are hotter on gold jewelry(than some PIs anyway), and you dont have to dig iron. I find it very hard to dig with a scoop more than a foot deep, especially in the water. It keeps filling back in. So to a beach hunter, depth is not good if it will go 2' deep on a quarter or a beer can bottom or hunk of iron. Rings always seem to be a foot or less. For me anyway. And that is what you usually are looking for.