I've read somewhere around here, possible the SP team board, that people have had the best results w/ the C4 cards running XY... I've been running DIN since I picked my C4's up and have been happy w/ the results but I just recently mickey-moused a riser to start running XY... I haven't tried XY yet, but I'll tell you what I think, once I have...
I hope that helps, probably doesn't, but you never know...