... Given that you don't have a discreet graphics card, nor any hard drives in the upper chamber, why on earth do you have all those fans in there? It strikes me as a bit of overkill. ...
i always try to build redundancy into my cooling systems, since i've had several system failures over the years caused by fan failures. with my strategy of "all components passively cooled; multiple low-speed case fans," any single fan failure should not stop or damage my system (i hope). i guess i would not disagree with the assessment of "overkill." call it intentional overkill.
Why aren't you using the CPU fan header? I'm also cooling a 125 Watt CPU + GPU with Ninja passive using only 2 anemic Noctua fans. I would not have been able to do that without thermostatically controlled fans. The Asus BIOS q-fan thingy ramps up the fans only when needed, but under normal use they run ~800 rpm which makes for a near-silent machine.
i'm sure all my fans are well under 800 rpm now. still, i may take your advice and try using Q-fan to reduce noise even further, while keeping the same number of fans.
one concern: CPU and northbridge temps are fairly independent of each other, but Q-fan only looks at CPU temp. so if you had a graphics-intensive program that used the CPU only lightly, Q-fan wouldn't speed up the fans, since the CPU would remain cool, even as the northbridge heated up from the graphics load. for this reason, i think i only want to let Q-fan regulate the rear-facing 120mm fan, which i think is the least necessary of the 3 fans in my system.
question: if you have fans plugged into the "CPU fan" and "chassis fan" connectors, does Q-fan regulate both of them, or only the CPU fan?