Well, my concern isn't the noise, rather the fan dying
If the fan dies I suspect the PS3 will get hot very fast, and if you don't notice it's very easy to get a YLOD within a few minutes, so I'd like to find the optimal value, which is still not bad for the fan, and the PS3 is cool enough!
By the way, Slim PS3s are also around 60C, aren't they? So shouldn't that be a safe temp already?
Fan will only broke if you leave your PS3 24/7 on (seriously as I said before, even with a stock fans in PC doesnt get broke after 5-6 years of nonstop use, also they also tend to break if you place your PS3 where humidity is high like near in kitchen where the nasty deposits may harm the fan bearings. Its a brushless fan and the spec of the fan is technically fit for speed up to 12volts which is equal value for FF.
Also PS3 wont turn on without fans rotating, it works just like what other modern pc right now, if the processor's fan doesnt spin, the BIOS will tell that there's something wrong with the CPU fan and it will be shutdown in few seconds. Same with PS3, though this time it will beeps with 2 and shutdown, not 3. Sony isnt that idiot that they forgot to put something that simple protection about fan not working error.