RAM placement confusion

[wdegillio]

I have read on a few Mac websites that the order in which RAM sticks (of different memory amounts) are positioned on the risers can affect RAM performance. Assuming that RAM sticks are added to the sockets in the proper order (as described by Apple), how should I install my new RAM for optimum performance? (I apologize if this gets overly geeky!!!) Here is my current configuration---

Riser A * DIMM 1 - 512 MB
Riser A * DIMM 2 - 512 MB
Riser B * DIMM 1 - 2 GB
Riser B * DIMM 2 - 2 GB
Riser A * DIMM 3 - EMPTY
Riser A * DIMM 4 - EMPTY
Riser B * DIMM 3 - EMPTY
Riser B * DIMM 4 - EMPTY

I just purchased 2 more 2GB sticks to bring my total RAM up to 9 GB. How should I position the different RAM values? Does it even matter??

TIA,
Bill G. Degillio
Mac Pro Intel 3 GHz Eight-Core* OS 10.6.2* DP 7.1

[1nput0utput]

A while back I found some PDF documents in the support section of Apple's website that explained exactly what you're asking. If you search for info about Mac Pro memory upgrades, you'll probably find them.

[newrigel]

Put the largest ram modules in the first pairs of the risers since they are accessed first.
Example:
Riser A * DIMM 1 - 2 GB
Riser A * DIMM 2 - 2 GB
Riser B * DIMM 1 - 512 MB
Riser B * DIMM 2 - 512 MB
Riser A * DIMM 3 - 2 GB
Riser A * DIMM 4 - 2 GB
Riser B * DIMM 3 - EMPTY (or the 512 MB)
Riser B * DIMM 4 - EMPTY (or the 512 MB)
Just remember, the largest allocations are hit first...