well... technically any knock is not reasonable, unless it's false which you will get, but as you tune you'll start to realize whether it's false knock or not. As for the tuning process you're gonna hit knock every now and then.. and when Josh and I were tuning my car back in october, we had 1 instance where if I even touched the gas pedal I was hitting red...
ended up pulling over on the highway, haha
Bio is right, most people keep it 5* as their limit. You're gonna see a lot of little 1* 2* 3* spurts at first. After you slowly dial in your tables it starts to disappear and you'll get your occasional false hits.