Sapphire HD 6990 4GB GDDR5 PCI-E DVI-I/QUAD Mini DP is a 30 cm long graphics card. Thanks to the 2GB memory buffer per GPU, gaming on 6 monitors should be a breeze.
As you already probably know, Radeon HD 6990 is the largest of the HD 6000 series, comparable perhaps only to the HD 5970. Our today’s sample is based on reference design but it comes with Sapphire’s sticker symbolizing twin GPU engine underneath.
Sapphire HD 6990 comes with a dual-link DVI out and four mini-DisplayPort (version 1.2) outs. 
Sapphire threw in a few dongles in case you require an HDMI or DVI connectors. Among them is the active single-link mini-DP-to-DVI adapter which can come in handy for connecting the third DVI display.
All the cards that launched today run at 830MHz for the GPU and come with 4GB of GDDR5 memory (2GB for each GPU) clocked at 5000MHz and paired up with a 2x256-bit memory interface.
Just like on the rest of the HD 6900 series cards, there is a BIOS switch that takes the card up to 880MHz for the GPU.
The central fan takes case of cooling where temperatures don’t exceed 87°C. Although the card is audible, it’s nowhere near unbearably loud. However, you’ll hear the airflow well.
Power Consumption
The card consumes around 37W in idle mode, which isn't half bad considering that a single HD 6870 consumes 22W.
On the other hand, HD 6990 consumes around 335W and if you intend to overclock it, you should know that it can draw up to 370W. This means that it will draw about 125W more than HD 6970, via two 8-pin connectors. 
However, all those watts aren't in vain and the card already boasts the title of the fastest graphics cards around.