Welcome to the X-Terra forum. I am in the US and also hunt for old silver and copper coins at old sites. Shortly after the X-Terras were released, I wrote a couple articles on coin shooting with the X-Terra. They can be found in the section above entitled FAQFAQ, or at these links.
http://www.findmall.com/read.php?55,288286,288286#msg-288286
http://www.findmall.com/read.php?55,497015,497015#msg-497015
Briefly, I like to hunt with my X-Terra in 4-tone, all metal mode. I ignore the low tones of ferrous targets and dig the other 3 tones that also provide a fairly stable TID. I find that the 3 kHz coil allows me to distinguish the sounds of deeply buried iron better than the other two frequencies. I like the 6-inch coils for trashy areas where target separation is important. My soil is moderately mineralized so the performance I get from the concentric coils is great. If your mineralization levels are higher, you may benefit from DD coils. I will run tracking mode if I am hunting on a smooth surface. If I am hunting a plowed field, I will use Auto GB and then set it a couple settings more positive. I run with maximum sensitivity most of the time. Almost to the point of becoming instable. I hunt looking for consistency. Consistent target location, consistent audio and consistent TID. I seldom dig targets that bounce more than two notch segments in any direction. I know I am probably missing some coins on edge or odd shaped pieces of broken jewelry. But that is the price I pay for not wanting to dig more trash. Just takes too much effort to get this old body up and down any more than necessary!
If you have any other questions, don't hesitate to ask. There are a lot of great folks here on the X-Terra forum. HH Randy