These are my impressions of the Thermaltake Silent Boost.
It's a piece of crap. Period.
My main objective was to get a hsu that would be quiet. Mission failed. This thing sounds more like a 60mm fan to me. And I should know how they sound, seeing as my last hsu was a Thermaltake Silent Viking (probably goes by another name in the US, but 21db/27cfm), which was not quiet either. So that's two Thermaltake Silent heatsinks I have bought now, and neither have been silent (or close to being). Thermaltake will not be getting anymore of my money, as far as I am concerned the rumours about Thermaltake and their 'insert bad language here' products are true. Cooling was however ok I guess, but as I said, cooling was not the issue. I have tried a couple of different Papst fans on it. At present I have a 8412N/2GML (19db/26cfm) on it. Funny side note here, is that that the hs can only hold two screws now. Apparently shifting fans a couple of times was more than the hs could manage. Booooh Thermaltake.
Reason I even bought it is because the Thermalright are very expensive here (Denmark). The SLK-800 is around $60. But in the end I did get my 80mm hs, I just wish I would have shelled out the extra, and bought the Thermalright. Or the Zalman 6000, which costs the same here as the "Silent" Boost. Oh well, live and learn.
Conclusion: If you are looking for a quiet hs, stay away. Get a Zalman/Thermalright, another 80/92mm hs of your choice.