I hope none of us are ever placed in that situation, but I don't think anyone can reliably state that they will put half their shots on target in a high adrenaline situation, most likely spurred by someone waking you up in the middle of the night.
Consider the statistical studies (unreliable as they may be) of police shootings over the past few decades. Generally speaking, most police officers have better training than the vast majority of us. Notwithstanding this, the "hit ratio" associated with police officers pulling the trigger is usually somewhere between 10% - 30%, and that sometimes includes officers committing suicide (pretty much 100% hit ratio there) and snipers taking someone out with a scope, both of which will drive that number up.
For example:
http://www.theppsc.org/Staff_Views/Aveni/OIS.pdf
Adrenaline and anxiety will do things to your body that even the best training can rarely counter. I've got 17 rounds in my M&P9 and 8 in my shotgun - I hope I never have to fire a single one in defense of my family. But I definitely would not count on putting half of those on target in the dark at 3am.