Looking into I/O junction from above the PCI slots, we can see there is plenty of room to get a second PCI Express graphics card into the second PEG slot. Of course we know we're going to loose a PCI slot if we go with a video card that requires two slots, but there is nothing behind the card that would interfere. Sometimes we find things like USB headers or even poorly placed SATA ports that can cause headaches for a second graphics card.

    While not many people may put a floppy drive in their PC anymore, motherboard manufacturers still insist on including the controller/connector. Regardless on how useless the floppy drive may be now, Asus has crammed the connector below the last PCI slot and in-between between an IEE-1394a Firewire header and a serial port header(another pretty useless feature). On the very outside edge, we find the HD audio front panel header block. A pretty typical place, so more than likely the wires in your enclosure will be plenty long enough to reach this.

     Once we get back up to the CPU socket behind the rear multi I/O panel things start to open up a bit. There are a couple of jumpers here for USB power settings, a 3-pin fan header and of course a 4-pin 12-volt auxiliary power connector.

     This should give you an idea on how much room you have to work with in choosing a heatsink for your CPU. One of my personal favorite's is the Scythe "Ninja" SNJ-1100. It's quite tall, but it also has heatpipes that extend outwards from the base that has caused issues with other motherboards. I'm happy to report that it does NOT have any space issues on the Asus P5N-E SLI.