Just to prove that no game can come close to Furmark temperatures, we also tested with the Lost Planet 2 Becnhmark, but we avoided the stock cooling due to the noise.
While Furmark maxed out with 81°C it's pretty clear that actual games will not reach such temperatures. With 69°C at it's lowest setting the Setsugen 2 is more than sufficient for cooling the HD6870.
At 1000rpm you get another 5°C off the card.
At full speed another 7°C are shaved off the temperature-scale.
As expected the 25mm does not do so well compared to the slim fan at full speed, but 61°C is just great for an inaudible cooling solution.