I have 2 of these available. I did remove the original heatsink to use the coolers from the Sapphire 290x tri cool cards. So the warranty stickers are no longer on the screws, but I've read that as long as the card is not physically damaged, they don't care about them. So I believe they are still under warranty.
I have a Sapphire 6990 with an aftermarker cooler by Artic Cooler. I had it Crossfired with a 6970, but then I upgraded to 680gtx SLI.
Runs pretty darn quiet and way cooler than stock. This will take up 3 slots when installed in a PC. I couldn't stand how loud the card got on the stock cooler, I had to install this cooler and it was worth it.