Im happy @ 3.8ghz. 1.5vcore is good enough. anything higher on air is not worth it. Waiting for watercooling.

But even then. 4ghz will take 1.55-1.6vcore. which is technically raping your cpu to . lol I dont believe 1.6vcore on any cpu is smart. doesnt matter how cool you make your chip. Its about the votlage going through it.