Another point I would like to make on this post. Others here have also mentioned this, but I'm not sure you understood correctly. If the SDC is going off on the hot iron rich rocks, the VLF will also, and much worse. Just because a VLF has discrimination doesn't mean it will ignore high iron rocks or even discriminate them out. High iron or heavily mineralized areas will likely in most areas cause a VLF to overload and won't be useable. Anytime a PI machine is struggling with the mineralization, any VLF will certainly struggle even more. Sometimes all you can do is just dumb down the detector, even with a PI.
I know an area where no current metal detector technology will function correctly. So much iron that any current technology will overload no matter what adjustments a person might try. Hot rocks the size of a chicken egg are no problem. Identify them, kick them out of the way and keep going. Little pea sized hot rocks are more frustrating as you have to dig them all up. So turn down sensitivity, slow down your swing speed, and get to know your machine. Happy hunting, Dennis.