[quotemsg=11626949,0,233449]Who puts a fan in the roof of a case to blow downwards? Surely the roof is best used as an exhaust and it was specifically mentioned about the fan blowing downwards. Personally I think I would be likely to buy a full set of fans so that I can fill all the fan mounts with the same design range and then keep the stock fans as emergency spares.
As for keeping the GPU cool, I don't that is an issue with 2 the fans in the front creating perfectly adequate airflow to keep the GPU cool unless you are using multiple GPUs. Although in time I would probably mod the window and inserting an extra fan there as that isn't a hard job to do.[/quotemsg]
in an idealist situation, the top panel fans should indeed be exhaust, but there are people in the rare occasion who want to focus on CPU cooling rather than the rest of the build, this generally calls for Watercooling with top intakes instead of top exhales. There's a moderately large temperature change when alternating the fans directions, the negative impact would be directly adding dust into your system, which can be cured by a decent air filter and regular maintenance.