Covering The Bases
We really couldn't ask for a better choice in slot arrangement or placement on a microATX motherboard. As you already know, Intel's Core i5 includes 16 lanes of PCI Express 2.0 on-die, while the P55 chipset offers eight lanes. The blue and orange x16 slots are tied to the processor, while the x4 slot connects to Intel's first PCH.
With one graphics card plugged in to the blue slot, that board gets a full 16 lanes. Drop a second board into the orange slot (which you can see in the picture is only wired for eight lanes) and both turn into x8 links. The x4 slot is open-ended, so you could feasibly drop a third graphics card into it for six-monitor support, or use an aftermarket storage controller. One PCI slot extends compatibility to older peripherals, though it bears noting that dual-slot graphics cards will block the platform's two other slots.