I just looked again using a Windows Search term of 'Guitar Rig' and found folders for GR 3, GR 4, and GR 5 at:
D:\Users\Bob\Documents\Native Instruments
And that is in addition to the location I posted a minute or 2 back.
Also, it looks like they changed some path mechanisms for the sub-folder structures at least between GR 3 and GR 4. For GR 4, the components (amps, effects, mic cabinets, etc) are contained in:
D:\Users\Bob\Documents\Native Instruments\Guitar Rig 4\Presets\Component Presets
While as I posted earlier the presets themselves are in:
D:\Users\Bob\Documents\Native Instruments\Shared Content\Sounds\Guitar Rig 4
I hope this helps more than my earlier post,
Bob Bone