In world of commercial beers, I think that there are actually two versions of RIS - the traditional English version and the American version. It's just like English and American Barleywines - the American version has a more neutral yeast and more hop character, and maybe a bit less body and malt character. The English version is more estery, a bit sweeter, a bit fuller-bodied and has more malt complexity. Think of the difference between Samuel Smith Imperial Stout and North Coast Old Rasputin.
For BJCP-sanctioned competitions, regardless of which way you go, a RIS has to be really emphatic. Full-bodied, lots of malt and hop complexity, possibly some pleasant aging notes, and detectable levels of smooth alcohol - but not cloyingly sweet and no solventy alcohols. It's a balancing act between making a big, impressive, solidly-engineered beer and one that tries to go to far and ends up with fermentation problems.
As others have said, RIS on the low end of the scale might do better in the FES or American Stout categories, especially if they don't have the body or malt complexity of a really competitive RIS. It's a common trick to brew beers that are just "a little to big for their breeches" for competition, since judges can't test for ABV.