The machine I have has an Intel 5520 chipset (enterprise equivalent of the X58) and Intel Xeon 5500 series CPU (enterprise equivalent of the Core i7 series). It came with 4 GB or RAM installed as four, 1 GB sticks. The chipset is designed to run in triple-channel mode, so the ideal way to install RAM is with 3 matched sticks at a time.
I wondered what happens when you install 4 sticks in the machine with 3 sticks filling one set of channels and the other stick installed by itself. In my case, because I am running 32-bit Windows XP, I can only address 4 GB of memory. This is an important limitation for me because between my video card (512 MB of RAM) and other devices, it leaves me with 2.93 GB of addressable space for RAM. That means I can remove 1 GB and still have the same amount of RAM.
The maximum bandwidth went up significantly under Sandra by removing 1 stick. Under Everest, the numbers remained close with 3 sticks edging out 4 sticks in 2 tests and losing out in 1 test.
So in the end, I pulled 1 stick out of my machine. I had the flexibility because I can’t use the full 4 GB regardless so I might as well take the performance improvement. Things will get interesting later this year (hopefully) when I upgrade to 64-bit Windows 7. The simplest solution would be to buy 6 GB (2 x 3GB).