Both are the same machine (Sovereign), but I've read a few say the Excalibur is not quite as deep or as sensitive to small stuff as the Elite or GT. I think the Excalibur was based on the XS, or at least the early version of it was if I remember what I read, but think somebody also said later models were based on a newer model. All the Sovereigns get outstanding depth from what most say. Just that the Elite seems to get a bit deeper, and many say the GT is a tad deeper yet and more sensitive to tiny stuff. I woundn't worry about whether the Excalibur is quite as deep as the GT, because the Excalibur is still pretty much the deepest VLF machine on the market for water/beach hunting, especially when there are minerals or salt present. If the thought bothers you that the Excalibur might not be quite as deep as the GT, just look into other coil options to make any depth advantage (if there is any) of the GT a non-issue, such as the S-12, 12x10, 15x12, or the WOT. All those coils should give you are depth increase over the 10" Tornado in most soils or sands on coin/ring sized targets, and now you are pushing well beyond even the best of VLF machines out there for the most part IMO.
I'm sure somebody like OldBeachNut or Mel Parker will chime in and nail down just what Sovereigns the Excalibur is based on and if they have any opinion as to it being as deep as the GT with the same sized coil. Just reporting what little I've read on that depth subject over the last few years, but I ain't read much on that, so I could have it wrong.