I would say that the title of "best fat twin" would be subjective and related heavily to the locale of the skier. In the west, in the softer snow, that title might be true of fat twins, but not fat skis collectively. A short ski like the PR, that is fat, yet easy to short turn can be the ideal for some, especially if the need for a nice flared tail comes into play. However, in heavier snow (crud especially) your G4 is going to kill it. It will be more stable at speed versus the PR, and plow through the muck better. Remember though, that the G4 is not a fat twin, so it cannot qualify for the best fat twin around.
I choose to ride a 191 10EX, which rides a lot like your G4. I love how it deals in inconsistent snow, as well as its superb high speed handling qualities. With that being said, I am looking to pick up a PR for glades and chutes (where I don't plan to straightline), to mix it up a bit. Plus, they are made to land fakie.
Basically, a PR won't replace what you love about your G4's, but it might provide a fresh new perspective.