To be frank with you, you could take just about any VLF to ironstone infested areas, and you will have trouble picking out targets from all the hots rocks, unless you have a well trained ear, especially hard with the magnetic ones. There are areas here in SA where detectors like the Goldbug pro, x-terra 705, probably the Scorpion, and even the GMT will have a lot of trouble operating there. Its all a matter of having the right tool for the job, PI machines for iron infested areas, and VLF detectors for working close to bedrock, pipe clay/spoil piles and quartz reefs (specimen gold).
I didn't mind the Scorpion when I owned one, the main things that bugged me was having to run 3 x 9 volt batteries, and having to open up the control box to change them out. What sensitivity were you running on the goldfields, it should be wound back until you gain a smooth threshold, otherwise you will simply be picking up too much of the background mineralisation?
Like the Whites Goldmaster series, they recommend to reduce threshold even by half or 3/4 to gain a smooth threshold in bad ground. There is also not much use using discrimination to quieten it down, as it utilises the limited internal auto ground balancing (used for coin shooting) vs the greater range of the manual ground balancing in all-metal mode. If you find the manual ground balance doesn't have enough range to cope with the ground, then I think you will find most other VLF's will also have trouble balancing or overloading on the ground.
If a detector running 15kHz is having trouble with the ground conditions, it is likely a high frequency vlf detector will have even more of an issue coping in the same ground. The manual ground balance has to be set up perfectly, and rechecked as often as needed in variable ground (including using the retune switch everytime you adjust the balance knob).
The smaller elliptical coil would also be preferable in hot rock laden areas, so you don't pick up multiple targets as you would with the larger coil.
I personally like the White Golsmaster detectors, as there is a fair bit of adjustability with them to cope with bad ground, escpecially with the combination of sensitivity control and SAT controls. Even the Goldmasters will overload in extremely bad ground, some areas in WA they are unusable, as you are unable to ground balance far enough to null out the ground mineralisation, I suspect areas in VIC would be the same.
As mentioned, there are sections of the VIC goldfields that will trouble all VLF machines, even the latest offerings, but the Garrett groundhog circuit has a long history in Australia of successfully finding gold, just not in all areas I guess.
