Overclock3D checks out the reference Radeon HD 6990 and awards it with a Performance rating. The card is the fastest single-card solution on the market, but unfortunately the stock cooling solution is very poor. The site complains they experienced more than one thermal shutdown during testing, and notes cooling doesn't really start until the fan hits a very high noise level.

It feels like it's been a long time coming, the dual-GPU HD6990. The reality is that it hasn't, rather our initial experiences with the current range of HD6xxx graphics cards from AMD were disappointing enough that it felt like we'd been waiting forever. So here it is in all its glory. Similarly to most dual-GPU single-board solutions we haven't got two of the top-end R6970 chips here, but rather a combination of two chips that would be a theoretical HD6960. Is this the card with which AMD reclaim the crown?

Link: Overclock3D