So I finally got around installing the gravity storm set into my rg920m. I also have the dominion/air Norton in my rg2620.
To be honest, the dominion is heavier, better for palm-muting, metal sounds. It is very similar to the Duncan distortion which is my fav bridge pickup.
The gravity storm is not as aggressive, a bit brighter (might be the guitar that its in though) - better suited for rock.
The neck pickup is nice - it is very clear and articulate - both clean and under high gain. I like it a lot, reminds of the air Norton (my fav neck pickup btw) but not as dark. It cleans up well with the volume knob.
Hope this helps, ask away any other questions,