Re: Fisher F5 11DD coil much better then the 10" stock coil
Depends on your soil. Minelabs use DD coils because Australia is high in Magnetite in the soil. So if you have a high iron soil a DD coil of similar size to a concetric would allow you better depth (ceteris paribus - all else being equal). Also in trashy spots a DD can be used to better effective depth than a concentric because it scans a area long but narrow. (c.p.)
To open the worm can - a good concentric is probably deeper than a DD of similar size and is easier to pinpoint with. But that added depth is only in the small center "sweet-spot" of about 2" diameter. The DD is deeper at the toe and heel than a concentric, so you don't need as much overlap to be successful. I like DD coils and once you learn their quirks they are handy critters. The 1" difference has little to add compared to the other advantages/disadvantages. Don't run out to buy an 11"DD coil if you have a 10" concentric (IMHO). Get a 6" sniping coil with the $ and you'll have a great junk area head for more flexibility.
