About graphics bandwidth:
They just did an detailed review to see what difference Intel's latest offerings would be because the newest CPU has built-in PCIe management but can only do 1xPCIe x16 v2.0 or 2xPCIe x8 v2.0.
The new ATI card, the HD5870 (currently the fastest single GPU card for desktop gaming) was used and it was determined that the x8 interface was NOT slowing it down). There is actually about a 1% difference but in reality you'd either be using the full single x16 or two in Crossfire but the bandwidth requirements in Crossfire aren't 2x (even in the CPU can keep up). So for the latest batch of video cards 1x16 or 2x8 (v2.0) for the PCI-Express bus is fast enough.
There is a lot of bandwidth in a slot even at "only" 4x PCIe v2.0. You can safely handle at LEAST a card with half the bandwidth (the frame rate is a rough guide) of the HD5870 which is the HD4870 or equivalent NVidia.
I'm not sure where you got your "x4" information. By all account this is an excellent board that offers:
1) 1xPCIe x16, or
2) 2x PCIe x8
Since the PCIe Controller is in the actual CPU this can't really change. This board can handle a Crossfire of 2x HD5870 1GB cards with no bandwidth restrictions.
While its true that the CPU controls the PCI-E lanes, the second slot has an electrical restriction which only allows it to run 4 lanes; it will slow a 5870 a bit, but probably not enough that you'd notice.
Just for fun, looks like these are all good answers. The real question lies in where you saw the information, obviously you used a utility that looks at your system and provides a report. Relying on Photonboys report about motherboard properties specific to your board I see Two possibilites. The utility your using is not current enough to see the real connection level. Your using another pci-xpress device which is eating up the available lanes which could downgrade the lanes available and or there is insufficient power getting the your video card which could force it to downgrade it's connection level. If you use CPUZ it will tell you whether your video connection is running in 16 lanes, 8 lanes or 4 lanes by clicking on ?motherboard tab.