only 4x7990 per Tyan B7015F77V4R ?

[KT819GM]

Regarding 6990 centrifugal fan - it takes air from it's top and blows inside into both directions, so front and rear heatsink gets cold air. AMD thought that it will solve problem like in HD5970 one gpu always hotter than other because front gpu already getting warmer air. But it was just too hard to make free airflow for 6990 rear part and because of that this 450W tdp monster heated whole chassis with trapped hot air.