If you are that concerned water cool it.a single fan wont save youForgot about this thread.
WRT the idea that a matching 2700 rpm fan, will only make 1-2 C of difference: I'm aware of that, but depending on the speed that may be the difference between throttling/not-throttling or going over 75 C and not going over 75 C (which causes fans to hit 100%).
These peaks happen a couple of dozen times a day and last a solid ten minutes, so it's not academic.
WRT to the idea that going from 2700 RPM from 1800 RPM will only make 1-2 C of difference: I haven't been taking notes, but I'm finding it's more like 3-5 C.
I'll post some pics tomorrow. It's a pretty standard 4U case with 2x120mm case fans in the front, and 2x80 in the back.