Riversoft Art at Daz3d has ones for G3-G8 and G8-G3, but I don't think he has one for V4-G8 as of yet.
This artist has one for Legacy to G3 and then G3 to G8:
Bummer. I don't know of a direct V4-G8 converter. I do have a tutorial for doing it manually that's worked for me when I absolutely have to have that, but it's a multi-step process that not everyone's going to want to attempt:
Iray does have the ability to render caustics from a refractive volume, but unfortunately it does not generate water caustics correctly regardless of the volume's refraction. With that said:
The basic water volume is a cube with a sculpted top surface in your modeling program and the refraction set to 1.33 and 100%. If you need color, then the thin-walled should be turned off and transmitted measurement distance used for color and turbidity (this is an absolute, not a relative value, so it needs a higher value the bigger the volume for any color to show up; lightness/saturation of the color plays into this too).
In products and renders of mine that use caustics in water, such as the Depths set, I used a flat plane off-camera with a caustic transmap and a light behind it to cast a caustic "shadow." The Depths includes this caustic light in the set. It's been a while, but I think one or more of my pool or Rigged Water sets do too.