I have a cheap powercolor AX7950 with a single fan in the middle of the card. Temps on the card were a constant 85+ at 100% fan when mining with a "normal" overclock. Since removeing the plastic housing temps have dropped to 75 on average and I can reduce the fan speed down to 70%. I have concluded the shroud is merely there to look shiny.
I have a sapphire with a single fan that sits at 70 degrees with 70% fan.
I think quality of the card plays a lot into how well the cooling shroud is supposed to work. Key example is the Sapphire has a heatsink on the vram and an offset fan. The Powercolor card has no heatsink on the vram and the fan is located in the center of the card.
I did the same to my HIS reference 7950, same as your AX7950. The temperature dropped from 82 to 76c.
I did not try on my Sapphire 7950 as the temperature is just 70c.
