Most of the cases I have seen have custom holes cut into them
to allow the placement of a lot more fans. I use a special tech
bench that allows for an open case with my 5970 and I have a
desk fan blowing directly on it to keep it cool. If the system does
overheat you will lose shares because of hardware errors which
you do not want at all!! Here is a pic of the bench I use to give
you an idea:
http://www.cyberguys.com/images/prod_main/P54119a.jpg