You should do a little web-shopping, and make some decisions about cool versus quiet. Like guns and butter, you get so much Y with your choice of X, except that some options provide slightly better combinations.
For instance, watch the forum-gremlins come out of the woodwork when I invoke the fan-word "Delta":
Delta 92mm Fan
Yet this fan only generates about 42-something dB/A of noise and pushes about 72 CFM of air. We do not, however, know [meaning I don't know -- myself] whether this is a combination of motor or bearing noise and air turbulence, or mostly air turbulence, because there's a difference in "irritation-level" given the mix in noise-components.
🙂
Here's another idea that will bring out the gremlins. This thing is a combination ball-and-sleeve bearing, but you would rather have double-ball bearings for several reasons. It's rated at 50,000 hours MTBF, but generates up to 48 dB/A and pushes around 79 CFM of air:
Blue LED goo-gah Fan
Tune it down to 3,000 rpms, and the noise level is probably in the low 30's if that, but the throughput is probably still in the 60's of CFMs.
Vantec Tornado
Here, you get lots of noise of various types at all levels of CFMs. But -- you DO get nearly 119 CFMs of throughput. Check, but I think it's a double-ball bearing, and I'm also pretty sure the "life-expectation" or MTBF is 100,000 hours. Here, you can keep your computer very cool in total happiness if you are a student at the school for the deaf.
Now take a look at this Panaflo:
[High Speed Panaflo 'H1']http://www.sidewindercomputers.com/pa92hisp.html[/L]
It only has a throughput of 57 CFMs, with a noise-level around 35 dBA. I would almost guarantee that the noise is more turbulence than motor-torture.
You can find the "L1" Panaflo on the same web site, or you can check "FrozenCPU" or "BuyExtras" or any number of places to compare fans.
There MAY BE A POINT in conjunction with the XP90 or any other cooler where more CFMs do not buy further reductions in temperature. You can pretty much assure yourself that fewer CFMs will lead to increases in temperature, even as the slower fan speed will lead to decreases in noise. Personally, I think you're better off with a range of speed and CFMs for any given fan you choose, but that means, in some cases, you either have to change the fan tail from 12V to 7V, or buy a fan controller. And if you change the tail, you really can't change the CFMs and RPMs on the fly, now, can you?
Remember also that the XP90 comes with silicone-rubber grommets to deaden fan vibration transmitted through the CPU to motherboard to computer-case-sounding-board. And further, the CPU fan is almost dead-smack-center inside the computer case, and that a "closed" computer case (without a CPU blow-hole) will cut the noise significantly.
Shop until you drop!!