On what RAM is supported depends on the motherboard as well.
For the Phenom II (socket AM3) chips, there insn't much point going beyond 1866MHz / 1600MHz.
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Phenom II X6 1090T @ 4.1GHz // ASUS Crosshair V Formula 990FX // Sapphire Radeon HD Dual-X 7970 // Thermaltake Frio w/ push-pull (using Antec Formula 7 Nano Diamond paste!!) // 8GB (2 X 4GB) G.Skill RipJaws DDR3 1600MHz @ 8-9-8-34-21-1T // Corsair TX850 850W // Corsair Force GT 120GB SSD (OS) // Kingston 200 V+ 120GB SSD // WD Caviar Black 1TB // Windows 7 Ult x64 // Logitech X-540