I have a 2.66 Ghz Quad-Core 2009 Mac Pro (4,1) which takes ECC (error correction) unbuffered DDR3 PC3-8500 (1066 Mhz) with thermal sensor. I read that while registered/buffered RAM is one cycle slower it more than makes up for that by being faster when working with other RAM sticks. I planning on getting 8GB x 3 = 24GB to keep it at triple channel. I read that registered/buffered will work. If cost is not a factor, should I hunt for and get registered/unbuffered? How much should registered/unbuffered cost over unbuffered, 25% more? By the way, CL = 7 thus CL = 7 = 1066 Mhz? I also read that I can buy 1333 Mhz RAM and my Mac Pro would just down-grade the speed to 1066 Mhz. Is there any down-side to getting 1333 Mhz RAM? My 2009 Mac Pro has a 12 rank maximum, correct? What's better RAM, Quad-Rank, Dual-Rank, or Single-Rank? Since I have a single processor Quad-Rank is bad if I use 4 sticks since 4xQuad=16, which would go over my 12 rank maximum? Thanks for any help!