Radeon users: Catalyst 10.9 through 10.11 + SDK 2.1 seems to be the golden combination for 4xxx and 5xxx miners. Catalyst 11.5a + SDK 2.4 seems to be golden combination for 6xxx. 2.4 does not suffer from the CPU use bug 2.2/2.3 have. Do not use 2.2/2.3.