I gave this scene a shot today.
I did one of my usual tricks of doing separate passes for general lighting and caustics.
The reasoning behind this:
* Point lights generate the sharpest/fastest caustics, but are not suitable for general lighting of your product.
* HDRIs with multiple 'light pins' (which is probably what you want for HQ jewelry/fashion ware) cause caustics to take a long time to converge.
Attached is the result after compositing in Photoshop.
Here you can download a zip containing:
* KeyShot packages with scene files for both the base and caustics pass
* EXR renders out of KeyShot (base & caustics)
* Photoshop working doc
* Final image
I did this really quickly.
You can get better results with some more tweaking in KeyShot, more render time and better compositing.
I hope this is what you're looking for...

At least I had a lot of fun taking your scene for a spin!

Dries