What voltages should I not pass using this cooler? 1.3 volt on vcore, some May recommend higher but I would not recommend higher for 24/7 use.
What clock speed on i7 4790K can I expect to achieve ? 4.7gHz seems to be the normal stable achieved for 24/7 stable use.
what are the chances of my h115 leaking? If you follow the installation instructions and are careful the risk is very small. If you are worried you can put some paper towels around it the first time you run it as a safeguard.