Beats most hydro coolers in benchmarks. I think the corsair h100 is the only one that is better but only by a degree or two.
This may not be the absolute best but it is the one that I use. I am only saying this because someone is likely to find some benchmark somewhere with a new cooler that I have not heard of that beats the noctua by a degree or two.
It is a bit pricey but I replaced my antec620 hydro cooler with this for two reasons.
1. Under full load it runs 4 degrees cooler than the Antec.
2. It looks cool as hell.
I have a good benchmark linked on my desktop computer that shows the noctua along with about 12 other air and hydro coolers including the antec920 and the corsair h80 and it does a slightly better job than both of them. I am currently setting up a raid on my pc so if all goes well I should be able to link that benchmark tonight or possibly tomorrow.