Ok, let's look at that fan again (the one in the first post):
http://www.deltaww.com/products/dcfa...B120120254.pdf
It's rated for 12 Vdc (7.0 to 13.2), 1.45 amps, turns at 4'000 rpms and...
will deliver a max flow of 150 cfm, and deadhead at 0.489 in H2O.
At .25" H20, it'll do almost 120 cfm. It will however, hit a noise level of 56.4 dBa.
That being said... I believe that 4 * 60mm fans should make less noise, but I think that we're still debating that one... I plan to test with 9 * 40 mm fans (when I have time), maybe it'll clear up the issue... Either way, a blower (squirrel cage type fan) is quieter, but can be hard to find. It is however, a common car part...