Thanks

Maybe after Roundup 3 I'll go back and retest with dBA numbers...I feel like I should with what I've learned about the Slip Stream

I feel the S-Flex series is as solid as it gets for...almost everything. Going into Roundup 2 I just thought they were a victim of "internet hype" but they turned out to just be really solid performers It may not be the best at everything (it usually isn't--there are no fans like that though), but it's always close and its S-FDB bearings are pretty darned good too.

The S-Flex F also holds claim to one of the biggest dynamic ranges of performance--it can go really slow and quiet at low voltage or it can go up to 1600RPM and move ~61CFM. Most fans that move 60+CFM don't ever really quiet down fully (you've noticed this and mentioned it a couple posts up too ).

Inferring from the lack of increase of noise on a radiator with the S-Flex E, I'd feel it'd perform great on a fan filter.