Check the depth of the fan and the noise rating. I'd suggest a fan with a noise rating of 20-26dB(A). Much less than 20dB(A) won't be worth the probable extra cost unless you are going to modify the shape of the holes in the lid. Beyond about 24dB(A) will be increasingly noticeable in a quiet room or with the engine off. You'll almost certainly need to modify the drive bay if you use a 20mm deep fan. 12mm or 10mm depth will be okay. 6mm deep fans tend to be a bit quieter but have less surface area so can't push quite as much air around.