From page 10 in the EP45-DS4(P) user manual:
- (Note 3) If you are installing one PCI Express graphics card, be sure to install it in the PCIEX16_1 slot for optimum performance. When both of the PCIEX16_1 and PCIEX8_1 slots are installed with expansion cards, the PCIEX16_1 will operate at x8 mode.
- (Note 4) The PCI Express x4 slot shares bandwidth with the three PCI Express x1 slots. When it is populated with a x4 card, the three PCI Express x1 slots become unavailable.
Note 4 is somewhat vague and it looks like you have a choice of using the x4 slot or all three x1 slots, but not at the same time.
It looks like using the x8 slot will reduce the upper x16 slot to x8 bandwidth for your video card.
The EP45-DS4 board has bios versions from F5 - F10b.
The EP45-DS4P board has bios versions from F3 - F9a.