hello, I want to buy 16GB RAMfor my 2006, 1.1 (2.1) MP DC device, with 8GB ram (in all risers) so i can install ElCapitan. I found some ads, selling either 2 DIMMSx8GB or 8 DIMMSx 2GB, PC2-5300x 667mhz RAM. Which one is best and possibly work faster, or it does not matter at all... What the term i.e. 2Rx4 means ? What is difference from 5300G, 5300F ram. Can xxxxG and xxxxF RAM work ok on my mac? Further machine info is: Kernel version= darwin 11.4.2, with secure virtual memory dual core xeon 80486, 2.66Ghz. Bus speed 1.33 ghz, SMC 1.7f10 Riser card s/n 922-7695 FB DIMMS 1GB 661-3930, FB DIMMS 2GB 661-3931 manual says i need RAM @ 667mhz, fbdimm, 240pin ECC, 36 devices max per dimm. not sure if needs FB or unbuffered.