If this is true, this fan would be perfect, but can I trust their testing/marketing?
Probably they're a bit optimistic, but - I guess - not by that much (it's a datasheet, not a marketing brochure).
What it's unclear to me is whether you will ever use them at 5k rpm, or not.
About noise, personally I can stand my 80mm fans running at about 1600rpm (Nexus and Coolink/Noctuas) but I won't call them quiet, just bearable: what you can't be sure about, it's the relevant performance.
The Sanyo-Denki datasheet states a mere 15.5cfm at 25%: they probably can be less noisy than your current Panaflo at 1900rpm, but IME/IMO you can't cool down that much, with such an airflow.
So if your problem is the actual airflow, I don't think a quieter fan would serve you better; otherwise, if your main concern is noise, IMHO you shouldn't need a very fast PWM fan, but just a better sounding one (a Nexus Basic or an AC F8 is what I would look at, Noctuas are also good, but they are quite expensive): but IMVHO a good sounding 80mm fan usually can't go as fast as 5k rpm, so it'd be a pointless quest.
At any rate, I would give a look to the ADDA catalogue
, looking for some suitable 2.5/3K fan, if any.