<< Dual link has twice the bandwidth of single link, however I do not know of any monitor that supports dual link. >>
Gosharkss, once again, hit it dead on. Twice the bandwidth, but no monitors nor projectors currently support dual link. However, since the price of the cables are identical (or practically identical), you might as well buy dual link to help "futureproof" your purchase. This is definitely the case if you're putting the cables in the wall (ie. between your computer and your ceiling mounted projector).