[killernoodle]

Do you know the difference between concave and convex?

Think Concave as a Cave. It dips in with high points along the edge.
Convex is higher in the middle than on the edges and is much more desireable with cores because there would be better heat transfer over the core.

Either way it shouldnt matter that much unless the difference was astromomical. You can always re-shape the heatsink/waterblock to fit the graphics card because I imagine lapping the GPU would be tough to do right.