I personally use Scythe S-Flex
fans, specifically the "F" model. Those are 28.0 dBA for 63.7CFM. I have two on my side panel as intake and one in the 5.25" bays for the same. The top side-panel fan is ducted directly onto my SI-128, such that the SI-128 essentially gets outside air. The bottom side-panel fan is ducted onto the intake of my HD 4870x2. The top has an exhaust Scythe Kama-Flex 80mm
running at 30 dBA / 34 CFM. There is another on intake on my hard drive bays. These are the loudest fans in my case, but I can hardly hear either of them during normal operation as they are behind several layers of plastic grating. Lastly, I have a Scythe Kama-Flex 90mm
running at 27.5 dBA / 37 CFM for my rear exhaust fan. The HD 4870x2 doubles as an exhaust fan due to the design of the reference cooler. Lastly, there is passive ventilation out the bottom of the side panel to prevent a pressure issue.
What does this massive block of text do? Well, 1) gives my raving support of Scythe's fans' performance/noise rating and 2) gives you a system that I find cools well for me. Given that you have a tower cooler and not a blow-down cooler, the idea of ducting your cooler directly outside will likely not work. Unless of course, you can spin the cooler 90Âº such that it faces the rear of the case, something I do not believe the A8N32-SLI can do. At least, not without a special custom retention solution from Hueristic.
(I do not know about the Slipstream, but I know my Silverstone FM-121
110 CFM fan is intolerable.)