I have read that it is a bit loud, is it true? And how good will it cool 7870, what do you think?
I'd say it's not much louder than similar setups (though surely louder than a water system, like the KrakenG10+H55 in my system). It's fairly quiet at even 100% fan usage.
As for cooling, it kept my r9 290 in the 60s, usually. So it should keep that card much cooler.