The title says it all: I'm looking for quiet 140 mm case fans that can provide a good airflow while staying nice and quiet. SPCR recommends fans up to 120 mm only. From an X-bit Labs article, I was thinking about :
- Thermalright X-Silent 140 (I'm already using some, they're quite nice)
- Thermalright TY-140
- Scythe Slipstream 140
- Noctua NF-P14 (because I will get some anyway with the CPU cooler I'll buy)

Thanks for your opinion!

Here's another 140mm fan roundup in googlenglish.
be quiet SilentWings 2 , Bitfenix Spectre Pro , Cougar Vortex HDB , Deep Cool UF 140 , Silenx Effizio and Thermalright TY-150 are recommended.
I've heard good things about be quiet Silentwings, but I'll probably replace my 120mm Scythe S-flex with a TY-150. They are very quiet, move a lot of air, start at under 5V, scale from 500rpm - 1200rpm and have a high quality motor (Sanyo, I believe) and high quality bearings (double ball bearings, potentially not as quiet as fluid bearings but apparently better for longevity).
They have unusual mounting holes in a 105mm X 125mm pattern (120mm fans have 105mm hole pattern, 140mm fans have 125mm pattern, I think).

The best 120mm fans are better than the best 140mm fans.

SPCR has had kind words about the Noctua 140mm fans (which can mount on either 120mm mounts or 140mm mounts)

I suspect the the Noiseblocker 140mm are as good as the Noctua 140mm, but I have never done an A/B test on that.

Interesting. Granted, the only SPCR recommended fan ranges that scale up to 140 mm are the Noctua and the Scythe, so they could be expected to behave about as good as the other models of the range.

The Scythe mounts only as a 120mm fan even though it is 140mm fan. For some reason the manufacturer's estimated lifetime is abysmally short... with the newest version being even shorter than the prior generation. I have a prior generation Scythe 140mm and I used a few times. It wasn't bad... but I don't think it is in the same class as the Noctua and the Noiseblocker... though it is much less expensive.

I've tried a gazillion fans by now and the Silent Wings (BeQuiet) are the best.