I have used a heatsink with a TMD 70MM fan before, the fan didn't make that much noise at all. This was on a Vantec Aeroflow, and the only noise it made was the sound of the air moving, pretty much.
As far as decent 70MM fans go, though, you are right, the pickings are rather slim, especially if you are looking for quiet. Alot of times, the only way to get a quiet fan is to sacrifice performance. Some of the quietest fans around are the Vantec Stealths (80, 92, and 120MM only, though). They don't spin at that high of an RPM, and as such don't move too much air compared to louder models. But they are very quiet.
As far as finding a good fan for that 70MM heatsink, you may want to search around for an adapter to attatch an 80MM fan to the 70MM sink. They do make plenty of those. Just do a quick google, or check your favorite retailer to see if they have them in stock. You're gonna want to make sure you have clearance for the added height of the adapter and the 80MM fan, though.
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