Hi everyone, I am contemplating purchasing another coil for my 705. ------ Primarily would be used for seeking silver coils in heavily hunted parks. Depth is critical.-----Should I go with the 15" Minelab coil, the 15" Coiltek, or a NEL Thunder type? Not interested in a multi frequency coil. (already own a 10.5" DD, 7.5) ----- Any suggestions.......Thanks!