So, Minelab's marketing promotes FSB:
FBS is Minelab’s patented multiple frequency metal detection technology. FBS transmits a broad range of 28 frequencies from 1.5 kHz to 100 kHz. The increased frequency range allows FBS technology to offer more accurate target identification, improved depth of detection and improved sensitivity. FBS technology can be found in Minelab’s E-TRAC and Safari metal detectors.
Wouldn't that make it a good candidate for a gold detector. Or is having too many frequencies, too much and too broad, for hunting specific gold? You mention Iron and Ground Phase, perhaps these models are lacking in that dept, unlike a gold-specific model.