Research (.pdf alert) from the Centre for Creative Leadership has found that members of the c-suite who demonstrate integrity also perform well; however, the same is not true lower on the totem pole.
The centre examined data from 191 top executives and 246 middle managers to determine the importance of four character traits: integrity, bravery, perception and social intelligence as reported by themselves, their co-workers and their board members.
As an indicator of good performance for top executives, integrity topped the list. For middle managers, however, integrity came behind social intelligence.
The lesson seems to be, then, that you can backstab your way to the top, so long as you leave the knife behind once you pick up that title.