Memory selection for Xeon W5580

Hello,

I have purchased a Dell T7500 workstation which has a single W5580 CPU and 6 DIMM slots available. I initially plan to run a 32-bit O/S on this particular PC but eventually will migrate it to a 64-bit O/S. My question concerns selecting the proper memory for it. Looking at the 5500 series memory rules it seems that if I were to populate all 6 DIMM slots the max memory speed will be reduced to 1066MHz (because there would be two DIMMs per channel). Thus to keep the option of running 1333MHz memory I would like to populate only 3 DIMM slots.

Since I initially am going to run a 32-bit O/S I only need to have about 4GB memory. So, between these configurations would I likely see any difference in system performance if I populate the DIMM slots like this (assume all DIMMs are 1333MHz):

1) A single 4GB RDIMM (utilizes 1 channel - allows for 2 additional 4GB DIMMS later for a 64 bit O/S)

2) Two 2GB RDIMMs (utilizes 2 channels - allows 1 additional DIMM for 64 bit O/S)

3) A 2GB RDIMM + two 1GB RDIMMS (utilizes 3 channels but would require replacing DIMMs to have more memory available)

Also, are there any advantages/drawbacks to using UDIMMs if I use only 3 DIMMS?

Thanks,

-Ray