you can either do a softmod like the one you've got going now or you can hardmod the card such that the fan is controlled by the temperature and isn't constant. hardmodding the BIOS just requires you to edit the fan trigger slope, which will help you keep the card quiet and keep the temps down... i found that around 40% fan was good to keep the 4800 series cards cool and wasn't too loud with the stock fans, but during gaming I had to turn it up to around 65%, which got a little bit loud, but not too bad...
first of all you'll need to grab your BIOS from the card using WinFlash (which you can get here ->
techPowerUp! :: Download Winflash 2.0.1.2), which you can also use to flash the BIOS later on.
you can mod the BIOS using Radeon BIOS Editor (which you can get here ->
RBE - Radeon BIOS editor)... i'll make a couple of recommendations for the mod... for your boot clock values, use the defaults with default voltage... for the 1,4 and 7 values (that is your 2d clocks) use something like 250/450 with lower voltage... this will help to lower the temps you get in 2D modes... you can probably leave the rest as is, or you can lower the clocks and voltages for the 2, 5 and 8 values (your low 3D clocks) and even raise your 3, 6 and 9 clcoks (to OC your high 3D performance)... then move to the fan settings tab and set your Tmin to 35C and your Tmax to 90-95C... then set your duty cycle to 35-40% which will keep your card cool while idle... now just save the BIOS and flash your new BIOS using WinFlash
there's currently no aftermarket air coolers for this card, but there are a couple waterblocks if you wanna set up a water cooling system, but the blocks themselves are quite expensive, and a simple fan mod will get the job done just as well
a few reasons i recommend a hardmod is because it will work for you if your working in the mobo BIOS, you can lower/raise the clocks and voltages for cooling/performance purposes and you won't have to change anything when you start gaming
hope that helps you out... and if you need any help, drop me a PM whenever you need