Garretts aren't the deepest machines out there, and I don't think they were designed to be. But they are so much fun to use. Turn on and go. The extra bells and whistles on the 1500 and 2500 really make coin and ring finding so easy. Once you understand their limitations, and what they can do, finding coins, tokens, rings, whatever have-you is like taking candy from a baby. However, there are machines that go deeper, and so what. Probably over 90% of the coins dug are in the 0-6 inch range. Ever tried digging a 10 inch hole in a park or blvd? Bad PR. If however you do a lot of digging, say in farmers fields or the woods, then by all means, shop around and get a machine with a large coil. Just some food for though. It's a tough decision. I think a good part of the answer comes from the type of mineralization you have in your area.
My deepest machine is a modified Whites Surmaster II machine. I only use it in the water though. It just doesn't give me all that information that the 1500 does. Not near as much fun. To me depth is only part of the picture. Hope this helps Brock. Good luck with whatever you purchase.