I like Gigabyte's NB heatsink design better. They actually cut away the part where the add-in card would go (on my 790GX, I'm using my sound card in the top slot). A lot of people think that it hurts the chipset cooling, but it's quite the opposite. It means that the air from my CPU cooler, which is pointing upwards, is actually funneling air around the NB heatsink creating a wind tunnel.

Besides, NB heatsinks have a huge thermal threshold. Really, there's no reason for Asus to cut that slot off.