Where Eventerdrew is coming from, is the article Jim Wofford wrote in the Practicle Horseman Magazine where he discussed the high rate count of accidents that have been occuring on the CC course in Low Level Eventing.
These fences don't play games. Period. He stressed that over and over and one of the things he discussed, amongst other important point factors - is that if you cannot ride a stadium fence solidily, you have no business going over a CC fence. And he also said that if a riders form is insecure over a CC fence they need to go back to the arena and work on solidifying their form over a Stadium Fence.
We say this not to be mean but because we are concerned for your safety. I agree with Eventerdrew, you should be really focusing on solidifying your form before you even think about going over N fences - or you will get hurt.