Dual Graphics VS Single GPU

[smeogan]

Hello, I have a question.

In my computer, i installed an A8-3870K overclocked to 3.5GHZ Apu that has an overclocked Core clock to 960Mhz and 800Mhz Memory clock 512Mb DDR3 integrated Radeon HD6550D GPU (OCed both by the bios) that i CrossfireX Dual Graphics with my Radeon HD6670 Core clock to 800Mhz and 1000Mhz Memory clock 1024MB GDDR5 which makes a called Radeon HD6690D2 GPU with unknow Core and Memory clock speeds..

According to this review: http://www.rage3d.com/reviews/video/sap ... ex.php?p=4 the so called HD6690D2 is a way better than the HD6670 alone; for gaming i presume?! But Windows 7 experience index gives to the dual graphics HD6690D2 a 6.7 in both graphics evaluation, and it gives a 7.1 in both for the HD6670 alone.

Both ways have OpenCL and DirectCompute 5.0 options

My question is:

Which configuration is better for video editing/rendering etc (whatever i can do) with "my rig" for inside Corel VideoStudio Ultimate X7?
The dual graphics HD6690D2 or the HD6670 alone? And why?

Thanks for your answers!