pci express help wanted!!!!!!!

Hi, i have a rampage formula motherboard with a chipset of x48 but the back of my motherboard box says chipset x38 and i have a hd4870x2 which i am having performance trouble with (same performance as my old 8800gt, if not worst), i installed a program called sandra lite which was recommended my a friend, and when i do a test on my motherboard and choose info about an pci express slot (which i have 2x 2.0 @16x) the details come back as pci express speed 5.0GB/s.

Does this mean my slots are only running at 5.0Gb/s (instead of 12.8GB/s or whatever 2.0 run at) using my hd4870x2 (which might be the reason why rubbish performance) or is this info correct?

help me!!!!!!!!!!!!