I've already seen a few reviews out there suggesting that the 1000rpm Ultra's were duds (the 2000 and 3000 rpm versions aren't bad though), but this really puts it in context. Heck, a single Noctua beat TWO Ultra's on the radiator.
The reason why the Ultra Kaze fans aren't bad operating at 2000 and 3000 RPM is because they are operating faster than most of their competition. If Noctua bumped the speed to 2000RPM it would have the potential for some SICK performance.
How big of a difference was there between the Noctua and the YL? I've got 1200rpm YL's on the my PC, and they're the noisiest component, so I'd be interested in something that could quiet things down a little more without sacrificing airflow.
I would say the difference between the YL and the Noctua in terms of noise output was pretty extreme. I have become used to my Yates and I only realized how loud they are after installing the Noctua. If the Noctuas are too loud for you, you can just use the LNA (resistor) that is supplied with it to bump RPMs down to 1000.