The speed of fans in PS's are controlled by the PS. They only run at their maximum speed if the PS loaded close to its maximum rated power. I would be inclined to get the 1850 RPM version of the Gentle Typhoon unless you were very sure that you would run it near its rated capacity, or at elevated ambient temperatures.
I'm not a gamer and my system specifications:
 Processor: Intel Core i7 920 (overclocked at 3.6GHz)
 Graphic card: 8600GT 256MB
 Titan Fenrir V2 + GentleTyphoon
 Two 120mm case fans (current rating of each fan 12V/0.16A)
 Two Western Digital HDDs (500GB and 640GB)
 One LG DVD-R/RW
If I replace the PSU's stock fan with GentleTyphoon, I will run the GentleTyphoon at its 1450rpm.