I hunt curb strips with the Tesoro Mojave with the 7" concentric coil.
I use my 540 vanquish for just about everywhere else.
have been hunting for over 35 years and most of the ww2 and earlier coins were found at the 4-6" level with modern clad at the 1-3 " level "generally" occasiionaly will find coins at 7" but mostly infrequently. this has been my experience here in New England.

(h.h.)
j.t.