Perhaps you could approach it from a different angle.
You are insistant on a 2500rpm fan, but rpm is not really your goal. CFM is.
What CFM was the original fan? The Panaflo?
This might give you more options in regards to possible candidates.
Looking for reasonably quiet 92mm 2500 RPM fan
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Airflow alone is not reliable enough for me to set a benchmark on. Just as dBA, CFM can be inflated. It is almost impossible for most users to reliably determine the given airflow of a fan.
RPM is a lot more usable. Given similar conditions, amount of airflow is nearly the same regardless of blade design (unless it's exotic). RPM can be monitored. I will know if I'm not getting the speed I want. RPM can also provide some idea of its acoustics, as higher RPM is most likely louder than lower RPM from bearings of similar quality.
RPM is a lot more usable. Given similar conditions, amount of airflow is nearly the same regardless of blade design (unless it's exotic). RPM can be monitored. I will know if I'm not getting the speed I want. RPM can also provide some idea of its acoustics, as higher RPM is most likely louder than lower RPM from bearings of similar quality.