There are some who say the GT is deeper than FBS machines at least at certain sites due to some quirks of the two systems- FBS vs BBS. That might be due to the higher/more frequencies of the FBS machines picking up more RF noise or reflecting off certain ground minerals, or it could simply come down to the user and how he wants to hear targets at fringe depth. Also, I wonder why Minelab would stick an 11" coil on the SE and Etrac if they were already deeper than the Sovereign or prior Explorer models? There wouldn't be much point to doing that if they were, and they would have saved a bunch of money in production by just using the 10" coil they've always used. It turns out the Pro Coil is an awesome coil in it's own right, but again I wonder why it was necessary to step up to a larger coil. I'm probably wrong but I am suspicious that was done so that people would see a noticable improvement in depth over prior models. By the same token, one has to wonder just how deep an SE or Etrac would be when compared to Sovereigns and prior Explorers if they all went head to head using the same size coil. In other words, if an Etrac is deeper using the 11" coil than a GT with a 10", I have a feeling the GT using say a 10x12, 15x12, or S-12 might show greater depth by comparison.
I've found my GT to be deeper than the 3 prior Explorers I've owned in my soil, but that can also be due to the more stabile ID of the GT which is more directly tied to the audio. What you hear is what you see on the VID of a Sovereign, where as on other machines audio and VDI can be largely out of phase with each other, so it becomes more important to pay attention to the audio on them and not what the VDI is doing. I'd say the GT has the most stable VDI I've seen on any detector, even ones with much less resolution than the GT. That's important because often you trade stability (and thus the impression of good versus bad targets) for resolution on some machines. I know I always found myself questioning targets that turned out to be deep coins on my Explorers due to the ID which tends to roam more than what I've been used to.
More than anything what it came down to for me was that my Explorers would wear my body out as much as my mind and took the fun out of my hunts for me. Being able to lighten up the GT easily has made it lighter than my Whites now, and not having to second guess each and every little setting to get it running at full performance is easier on my mind. I'm the kind of person who tweaks and tweaks and second guesses each and every control on a detector. It doesn't have to be that way on the Explorer but that's the way I am wired, so as a result I find much more peace of mind without having all those things to tweak. The GT gives you all the control you need to max out depth and performance without as much risk of hurting yourself should you have something set wrong. If tweaking is your thing then you'll like the Explorer better. If you hate always hunting with that "doubt" in your mind that you've set a machine up wrong for a given site then I'd suggest a Sovereign. I also found the longer more drawn out audio on the Sovereign to be better for me. It reminds me of a Whites in terms of information you can pick out of it's longer audio response to targets, yet with the multiple tones of a Minelab to further discriminate targets out by ear.
That all being said I still love detectors with computer controls. Due to the better physical design and also a few internal features of the Etrac I may pick one up one day, but if money permits I'll keep the GT as my other Go-To detector. Based on user, coil, ground conditions, and settings, any one of these 3 machines can and will beat the others in depth on any given day. It's that close between them, and the outcome is more based on how you want a machine to respond for you. Some people like being instructed on things one way versus another, and I look at that as the main difference in the big three Minelabs. Find the machine that acts, sounds, ID's, and performs in a manner which is better suited to your personality and hunting traits. Based on that any one of these 3 will do better for you.
Now, since this is the Explorer forum let me put in my disclaimer to avoid at least some critical responses. I love the Explorer, I love the Etrac, and I love the GT. I don't care if any one of these three had some large flaw in quality or performance, the fact remains I'd still pick any one of them over just about any other detector on the market. Find which one of these three works best WITH you and you'll have no competition to worry about.