They should be around 20db in max speed
It would be a miracle if they could run a 92mm fan at 2500RPM with only 20dB. Maybe if you measure from the next room... I believe the noise level when MikeC has measured it.
Ceramic bearings is nothing new. In fact they are an older invention than the hydro bearings used in many Panaflo fans. I believe that ceramic bearings will degrade more than hydro bearings over time. Not to say that ceramic bearings are bad. Tests has prooven that they work about on pair with hydro bearings noise wise.
If I remember correctly many Papst fans use ceramic bearings.
Fan warranty is IMHO a marketing thing only.
If you nurse a fan well (e.g. dust filters etc) as you should (but very few do), then it will last for a long time. Note that even if the fan becomes quite noisy it is still not a case for warranty. It usually needs to fail to become a warranty issue. Even quite poor fans usually live at least 3 years before they fail.
Lets assume you have a crappy fan, and you stand the noise when it becomes worn. Lets say it does fail after 5 years. What is the chance that you are interested in an identical cooler after 5 years?
It is likely that you want a new CPU with a different CPU socket after 5 years anyway. So I would say it is safe for any manufacturer to give lifetime guarantee on CPU fans, as long as they are carefull on what they write in the fine print.