im choosing between a Phenon II x4 965 and an Athlon II X4 645 and the Radeon HD 6850 or the Radeon HD 5570 as a cpu and graphics cards for a gaming computer. the cases i have picked have 3 fans included. so do i need a heat sink with any of the CPu or Graphics Cards or will the built in fan be effective enough (including the 3 case fan and 1 fan in the PSU) to keep everything cool and prevent anything from over heating?