Join Date: Mar 2008
Location: Rochester, Medway, Kent.
I've always quite liked the idea of Chaotic GK, but I'm yet to come across a good reason for them fluff wise.
I suppose another reason could be they are a failed early experiment, thought destroyed but now they have resurfaced. A few thousand years of fighting in the Eye of Terror has made up for any deficiencies they may have had as 'not quite finished' Grey Knights, and although fluff wise they may be different stat wise they could be identical.
Chaos GK are always going to be difficult to pull off thanks to so many "I know that no Grey Knights have ever fallen to Chaos, these are the only ones." stories in GW and gaming clubs since the GK were invented.
Good luck with it though, I'll keep an eye on this one and see what people come up with.