I realize this is 2 years old and has been answered, but I have an H80i V2 and an i5-3570 non-K OCed to 4,2Ghz. I started out using the "quiet" setting in Corsair Link which maxes out at just under 2000rpm at 40°C for the cooling liquid, and even at idle runs at around 1400rpm. I then just went fixed% and picked the lowest value it would allow, 40%, which is around 1400rpm. Even under sustained load the CPU would barely break 60°C.
Finally I found out that setting a custom fan curve I could go as low as 25% or 900rpm, which is what it runs at 99% of the time now (I have it set to start ramping up pretty aggressively when the liquid breaks 43°C, but even at 100% sustained CPU load it won't unless the GPU is also running very hot for a long time, warming up the entire case), CPU temps still maxing out at 65°Cish.
tl;dr: You can go as low as 900rpm using a custom fan curve, and it'll probably be more than enough if you're not overclocking. Just make sure you have it set to ramp up if the liquid gets really hot (I'm not an expert but I'd think anything under 50°C is fine for any amount of time?).