The standard offset you can get these RG-R rims off of Tirerack are:
18

 

The difference would only be 4mm and they are 25mm per inch. If you want the more aggressive look run a small spacer and you acheive the same thing. I really don't think you would notice 4mm though.
If I can help let me know.

 

Are teh RG-Rs 1, 2, or 3-piece? If they're 3-piece, you can change the lips to pretty much whatever you would like.