I also have an M10, and with a correct PWM setup I believe this is the best you will do. I just installed this yesterday:http://www.amazon.com/Noctua-Low-Profile-Cooler-Retail-Cooling/dp/B009VY1PMI
The fan included is very quiet at low speeds, and the heatsink is much nicer than the crap stock cooler or the other little Silverstone low profile cooler I tried.
I set my PWM settings up in Speedfan to only turn the fan above a whisper if it hits 65 C or greater. This will be much better than a passive cooler: you have no course of action with a passive cooler if it can't keep the temps in check. I'm running a low profile 6570 in my M10 as well so it can get hot in there quickly. I did remove the fan from the 6570 heatsink and run it passively. To help heat escape, I installed a 92mm Noiseblocker Blacksilent Pro on the back/top vents as an exhaust. It's PWM controlled as well, the whole setup is VERY quiet and will only ratchet up the fans/noise if heat gets out of hand.
Watching movies w/ MadVR, my i3-2100 is loading at 50C and 6570 at 55C and it's basically inaudible from more than a foot away. My Plasma buzz is louder