From my experience I would say that it is unlikely you will get quite that high with just an H80i. I have the H100i and its great but even mine starts to get a bit toasty at 4.8GHz. What I find is around 4.8Ghz there's a bit of a wall in the overclocking and you have to pump alot more volts through it to get any higher. Of course this changes from chip to chip but I know a lot of people have found this at around this frequency. Im sure you could get there but it would start to get very hot by 5Ghz and I doubt you could do it without overheating the CPU quite severely.
I also find that the VRM get very hot for me, about 15C hotter than the cores themselves and this is what has been holding me back once you have to up the voltage a lot. You need a lot of air flow to keep them cool and especially with a small VRM heatsink like the one you have got.
So basically, it will be fine for maybe 4.6GHz but it doubt you'll get to 5GHz at all without damaging something.