I rode the first couple hundred miles in "C" mode, then bagged it and have kept it in A (or normal - it doesn't show up on the LCD screen at all unless you start pressing the mode buttons) since. C is definitely a dog to ride in - it's still a fast bike, but it does not spin up fast at all, A mode is like the hand of God pushing you down the road. It's what I remember about riding my buddies Hayabusa in 2001 when I was on my VFR800. I couldn't believe the difference in the effortless power. C and B modes detune it a bunch, A mode is where it's at.
Unless it's rainy, then I sometimes punch it down to B or C mode... A little more gentle seems better in those situations to me anyway, I've got less than 1K miles still (but close!) on the bike, so until I'm 100% comfortable with the handling I like the detuned motor if the roads are a little slick. At least for me it takes more miles than what I have on it to be completely accustomed to and comfortable with this bike. But hot damn, I love it!