What size gold are you after with a gold prospecting specific VLF in your area?
If you need fully submersible waterproof, the Equinox 800 with the 6" coil or the Nokta Makro Gold Kruzer are great prospecting detectors.
If you need lightweight, easy to pack and good selectable gold frequencies with a very hot coil, the ORX with the HF 9" is the way to go. There is a waterproof mod that costs about $60 that works well from what I've heard. Without it, the wireless signal can't get from the coil to the control box when the coil is submerged in more than a few inches of water.
I have used all three of these detectors prospecting. The Nox and ORX can also double as excellent coin, jewelry and relic detectors. In a pinch the Gold Kruzer can do that too but it is a single frequency detector (64kHz?) that is specially geared toward smaller gold and micro jewelry.
So if you are after smaller nuggets and pickers the Nox 800, ORX and Kruzer would work well.
If you want larger gold at depth the ORX and Equinox might be a better choice due to multiple selectable frequencies even though the Gold Kruzer like the others can go pretty deep on say a 1 gram nugget. They can all hit that in moderate to mineralized dirt at 6" to 8".
If you want to prospect in submerged moving water in creeks or rivers I would stay away from the ORX. It is so lightweight that if would be hard to control in moving water. The Gold Kruzer would be great at that and the Nox a close second.
For tailings piles with small gold or specie, all three would be fine especially on that blind spot area sized gold .1 gram up to .75 gram that the GPX 4500 can sometimes miss.
Jeff