Mobile graphics cards are really a different beast than the desktop variants.  Despite have similar names and model numbers, the specifications vary greatly as the GTX 580M isn't equivalent to the GTX 580 and the HD 6990M isn't even a dual-GPU product.  Also, getting the capability to do a direct head-to-head is almost always a tougher task thanks to the notebook market's penchant for single-vendor SKUs. Well, problems be damned, we had the pair in our hands for a few short days and I decided to put them through the ringer in our GPU testing suite and added Battlefield 3 in for good measure as well. The goal was to determine which GPU was actually the "world's fastest" as both companies claimed to be.