Hi I am currently running two hd-6990. They are extremely noisy and some time hot too. They do use lots of electricity. But bottom line is I am not at all concern about these disadvantages. I have good coolers of heat and a good sound system/Headphones. I play with 5760X1080 resolution. These monster cards are able to run all games on max settings.
I was going through some forums. Its was mentioned that a 7970GHZ is more powerful then a HD6990.