another question please... is it going to be greater? if use 2 CF cable in dual cf or is it the same result for single cable? many thanks
As far as I know, using ONE cable is sufficient. Also, connecting your cards in PCIe slots 1 and 3 make sense (for lowering temps) BUT be aware :
1. You will get a small performance drop (I think between 5-10%),
2. Make sure you change your settings in your BIOS (advanced>north bridge configuration>PCI express selector>x8 x8) Why? because if you dont, PCIe for slot 3 will default to a x1 bandwidth (ie terrible performance!)
Also, your crossfire connector will probably be too short. You can get one on ebay :http://shop.ebay.com/?_from=R40&_trksid=p3907.m38.l1313&_nkw=100mm+crossfire+connector&_sacat=See-All-Categories
I would recommend using PCIe slots 1 and 2 for MAX performance. If you're worried about temps place a couple of case fans (120mm) directly onto the cards and/or changing the fan profiles in CCC. This should help.
PS Thanks to the members who helped ME with this exact problem.