I've run some 3d Mark tests on my z8750 2nd revision Win and it is hard to say with any certainty if the fan makes a real difference in short bursts of intense games/programmes. The scores were not consistently effected by the fan speeds for me to conclude there's a correlation.
On the other hand, with demanding games played over durations of about 40-60 minutes, I have found that the CPU cores run 2-3 degrees lower. I suppose it is also not only about simply keeping the temperatures down but also allowing the clock to run higher without throttling. I've only ever experienced throttling on SWTFU2 (horribly optimised port) and I could play a little longer without throttling when I turned the fan up to high from low.
Honestly, I'm undecided on the effectiveness of the fan and I turn it off/med/high depending on how hot the device feels at any given time :p