I came from a HIS ICEq 3 hd 3850 blower style fan to a dual fan (like yours) hd 4870 (which is a heat factory, unless undervolt/underclocked). While dual/tripple fan keeps the card cooler, it spreads heat through the whole case (I had at most 5 degrees more). They are quieter than exhaust/blower style fans.
heat is not a problem right now, my gpu reaches a 73° celcius max after like 10 hours of crysis 3, cpu is barely touching the 70° mark even under hours of load. (3570k at 4,4 ghz and 7970 at 1150mhz)
Money certainly is a bit of a prob right now, soooo i could just go and populate every available fan mounting place with lower rpm fans, i chose the scythes because the ratings were the best. In the end it would be cheaper to get a load of cheap low-noise, low-rpm fans than spending a fortune.
Not at all. 750W is more than enough for this setup.