With the Sovereigns I find it one of the deepest detectors I have ever used, but it takes time to learn and understand them. You must go slow to get the depth as many of the deeper signal are just a change in the threshold you would never hear if you were swinging the coil fast. The Sovereigns are also one of the best IDing detectors out there even at some great depth you may find unbelievable at times. Many dont see this until you have used it and understand it, so dont expect it to pull those 12-15 inch coins out until you get to know it well and what it is saying.
On meters is where many will differ on opinions, but to me a good 180 meter is a must to learn the Sovereigns and it helps me to ID the deeper targets too and could be because of my real bad hearing too. I find when calibrated I will get a 179-180 for a copper penny, clad coins and silver. A 176-177 will be my IH pennies, some of the older wheaties and the new zinc penny. Nickles have a separate tone and can vary a bit, but most will read 144-145 with the war nickles reading up to 151 because of the silver in them. Now the meter will help doing the ID as some of the tones are too close to tell the difference in them. Some of the deeper targets with the older Sovereigns I seem to notice after 8 inches it is a little more difficult to get the ID to get to 180, but it can for a split second or trying to climb the same as the tones, so on the deeper ones I watch that ID as I am trying to get the best signal. On the GT it seem like it will ID deeper as it is more sensitive, but can false more on iron and find if you check it out from other angles you will see it dont repeat in the same area as before. Some of the real deep one like over 12 inches you never will get the meter or the tones to become correct, but you can tell they are trying to climb and enough to want to dig in the older parks I like to detect and why the S-1 SunRay probe is also a must for me.
I used to have a XLT too and seen other go to the Sovereigns and for the first while you wonder if you made the right choice, but when you get to know it you will be surprise what you have missed both surface and deep coins with the XLT, but like I say you got to get to know it and understand it which some can do in one day while others it takes a while longer. It took me a good 2 weeks to get comfortable so i was finding some great stuff and learned something new each time out with it. It was well over a year before I felt I had mastered it and could tell by the tones and meter reading if it was iron, a coin, a beer can or other trash plus could tell you the depth 95% of the time. There are places you have to go normal slow and places you have to go super slow swinging the coil to hear those tone changes of a deep target.