As I noted in another question, I replaced a 2.6 GHz Pentium 4 with a 3.4 GHz Pentium 4. Unsurprisingly, it causes my little Shuttle XPC to ramp up its variable speed Sunon KD1208PTB1 80x80mm fan frequently. That fan is rather noisy when running at anything above a low speed. It has a 3 pin connector. If I find another 80x80mm variable speed fan with a 3 pin connector, is it safe to presume the power management system will be able to control it? Looking at that Sunon model, I don't see anything to suggest it uses any sort of proprietary control mechanism.
Also, is air displacement per minute the main specification I should consider when looking for a quieter fan that will still do the job?