Well, if you're going for a quiet fan, I'd stick to an 80mm vs a 92mm even though the SLK-900a can accomodate the larger fan. After experimenting with various fans of all sizes and makes, I've found the 80mm fans then to concentrate more air towards the center of the heatsink where as airflow from the 92mm tends to get wasted off to the side. The best combination of performance and noise I've come across so far with my SLK-900a is the 80mm Thermaltake Whisper fan (ttf-8025a) which kicks in a very impressive 37 CFM of air while allowing only 30 dBa of noise.
I'd stay away from the Antec (or the brands) of "Smart" Fans also. The variable speeds are suppose to help control noise, but it really doesn't work as well as it's suppose to.