I think this is the scenario for case that isn't installed with VGA that uses blower style cooler which exhaust hot air through rear PCI slot ..

if all the cool air is drag to the top and rear exhaust fan ..

what else left for south bridge and graphic cards

hmmm ... VIZO propeller would only help to dissipate heats of graphic card but that could be achieved if there's left cold enough cold air from side vent or front intake ...

I'd rather use a exhaust blower to get rid of hot air through PCI slot opening with the help of side VGA vent .. .

at least that could cool off both GPU core and GC Memory ...

Yah something like those ....

but often such type of cooler is a bit noisy ... which is why I don't use it anymore since long long time ago ..