There is no comparison between the two coils when it comes to depth. The D2 will always win out. As mentioned, with a smaller field the 6X10 will do better at separating out surface trash. A lot of folks prefer the Eclipse 6X10 because it runs quiet and stable, but that is only because it is not seeing as much ground at depth. Learn to deal with a little more noise and you will do better with the D2 on old coins. The 6X10 is the right choice for jewelry hunting without question in my opinion. To answer your question directly, I think in average soil you would see a two to three inch difference in depth between the two coils.
Jack