"So when Jim has Harry do something insane (like Darkhollow on Demon Reach with the Black Staff)"

Uhm so when Harry becomes the most evil character we have come across in the Dresdenverse...

Ok so since pretty much book one Harry has been saying that 'magical muscle' wise his pretty much at the top of the food chain. Is there a cap on how powerful a mortal wizard can be, if so how does that compare to other (non deitic) beings, e.g Eldest Gruff, and does there come a point where ones power forces one to transcend ones mortality/humanity?