If you have a unit with two fans that otherwise is fine then it makes sense to just remove the 80mm and replace the 92mm with a Panaflo low-speed. A lot folks run their PSU's with just a Panaflo 80mm low-speed but the 92mm flows about 35% more air for the same noise or the same air for less noise depending on how much voltage is supplied. Use the PSU's thermal control if possible as it allows for even more quiet while maintaining a margin of safety over just fixing the voltage at 5 or 7V. Otherwise an external manual variable control like the $5 Zalman (5-11V) is an in-between option (not better than automatic but better than fixed).
If you are going to replace the unit then definitely rule out any lacking Active PFC and try to get one with one fan instead of two which by nature of the limited box size requires smaller heatsinks and other components which naturally require more cooling in the first place. It is self-defeating and contrary to efficiency and quiet (great for marketing though). Speaking of efficiency, that is one of the two primary benefits of PFC to the consumer (the other being reduced EMI/RFI) since it means lower electricity bills and generates less heat which is a byproduct of the power transformation and so again requires less cooling.
I agree with Jhhnn -in essence concentrate on getting a good quality unit. The fan is almost unimportant as it is easily replaced for a few dollars with one that is ideal for your setup. ExoticPC, Zalman, Nexus, Verax etc, all just use Sparkle/FSP with custom fans. Seasonic is different but clearly a cheaper design and their prices are not competitive. Seasonic and Antec both use graphs in their marketing to tout their thermal control compared to "typical" thermal control. However, I do not see any difference between this and Sparkle's literature except that they don't hype it. Antec also chooses not to offer PFC outside of Europe where it is required but instead prefer to contract to CWT for a couple extra dollars worth of external thermal fan control leads and independent 3 and 5V circuits which are of questionable value when modern systems draw the bulk of their power from the 12V line alone.
And that's all I know about that (well, not really but I have gone on enough)
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