Dangers of limiting fan-speed
Some quick research says that the i7 processor starts to throttle itself if the temperature range gets too high (around 91C) so you shouldn't have to worry about it provided your CPU temp stays less than that.  Mostly the fan speed is trying to keep it comfortable on your lap as best it can - monitor your temperature during one of these "intense sessions" and see if it approaches that threshold - if it doesnt, and stays more on the order of 60C, you're fine as far as short term CPU viability

Research:
https://superuser.com/questions/239230/what-is-a-normal-safe-temperature-for-an-i7-2600k-cpu
http://www.maximumpc.com/forums/viewtopic.php?f=38&amp;t=136130