If you have the space, the upgraded fans look like a very good idea - though a 6 watt fan isn't super heavy duty, it's probably a good bit more than the average factory fan and probably flows a lot more air.

 I ended up doing something similar with some of my HIS 7750 cards when the CRAP stock fans on those died - had some 60mm Delta fans left over from CPU coolers I don't use any more, so just wire-tied them to the HS and VOLLA!!!! 15 or so degrees cooler than the stock fans EVER managed - just had to plug them into a 12V "peripheral" MOLEX from the power supply, as there's no way the card itself was going to handle the power draw.

 My Sapphire 7750 on the other hand just keeps going and going and going *WITH* the stock fan......