You can't turn a GPX into a ZED with a different coil!!!! The...

You can't turn a GPX into a ZED with a different coil!!!! The ZED DOD coil design is needed to counter non-linear motion signals, nothing to do with sensitivity at all. Read the patents and white paper. The spiral wound coils don't give any advantage depth wise, why would they? and a DD will always be less efficient than a mono, mainly because the signal must travel further from the transmit winding to the target and back to the receive coil, and the DD is smaller than a mono of the same diameter. Notice that the guy in the demo sells the Detech coils and didn't compare any of the new spirals with the older bundle wound monos even though it is the obvious thing to do? What good is the video without it?
"9th inverse square law"!!!!!! Hilarious!!! Even if you did manage to get that right, a different coil won't change the way the signal falls off with increased depth so why mention it?
The detector technology can though. A normal PI obeys a (1/depth^6) law for large objects at depth but the ZED technology does much better than this. Like I said, you should read the patents and get acquainted with the new technology.
No one cares if you try to predict the share price but don't base your predictions on silly "science".