DCII TOP is looking good to me. Excellent two slot cooler and voltage control. How far beyond 1150MHz you'll get is mainly dependent on how good a chip you happen to get, but that cooler and extra voltage should get even an average chip to 1200MHz.
Most reviewers only overclock with stock voltage which is why most cards come up short of the Toxic. Most 280X's have a stock voltage 1.2V whereas Toxic comes with 1.256V.