A while back, out of desperation to cut down on my 1,1 Mac Pro's noise levels (since it seems louder than a 2008 Mac Pro, and louder than others have described their 1,1 Mac Pros to be), I bought an Arctic Accelero S3 passive cooler for my HD Radeon 5770. Well, it proved to be a nightmare. The mounting system's design was horrible, and I ended up snapping the screws necessary to hold it all together. Regardless, the thing wouldn't have fit properly into my first slot. What, then? It may seem childish... but, I took my 5770, did away with its housing+fan as I would normally have, kept the card's stock heat-sink on, and then super-glued the Arctic Accelero's included 2nd heat-sink on top of that (yes, I really went to such lengths). That heat-sink is just another giant piece of metal that's about the size of my entire card put together, so I figured that it would do its job. So far, while the card does feel somewhat hot to the touch, it may just be its nature (as it's an AMD card and I recall it feeling a bit hot--even with its fan on). In any case, it is currently working perfectly! I have been using my Mac Pro just fine since, and my fan RPMs have not changed. Anyway, I don't want to jinx it all, but it has (so far) gone just fine, and I couldn't be happier with the results. It's great to have this relatively powerful card back in. Maybe I'll update with pictures if I need to open my Mac Pro for any reason. (The machine is a bit hard to remove from its cubby.) But, anyway, rather than spending time devising a better screw system for the Accelero, I went the frantic route. It's a bit of a hack-job, but it could be enlightening to others(?) If you are desperate to block out that fan noise, maybe see if you can pick up a similar heat-sink to glue on top of the card's fixed, stock heat-sink. Due to the great airflow that the Mac Pro's PCI/HDD area receives, the card is likely to be okay! What do you guys think?