As a general rule of thumb, it's not a good idea to overfill you engine oil. Reason being, if the higher than normal oil level reaches the crankshaft height it then gets whipped repeatedly by that rotation creating lots of foam (air) in your oil. Then when your oil pump tries to suck through oil to supply the motor it's getting a lot of air and not oil, which is as we all know is not good for lubrication.

I'm sure a little more than normal is okay, but I'm not sure what the limit is.