I need help with potential Mac Pro RAM configs

[NEENAHBOY]

Let me preface this by saying that I read the "Understanding Intel Mac RAM" guide, but it's either too vague or I'm just stupid (probably the latter), because I still don't fully get it.

I plan on using the stock Apple RAM and a 4GB kit (don't think I need the power of the 8 kit just yet), probably from OWC. From what I've read, I think my particular configuration needs to be like this:

Riser A
2GB | 2GB | empty | empty

Riser B
1GB | 1GB | empty | empty

With this, A1 and A2 are the same, as are B1 and B2. Is this a correct arrangement?

Also, I get that full 256-bit access won't be available with this configuration. When the guide says there is a small speed benefit to doing this, just how small are we talking? Would it be worth it to just get four 2GB modules and stick the stock RAM in A3/A4?

Thanks for your help, all.

 

[CanadaRAM]

That config is correct. A1 A2 - B1 B2

 

[hajime]

I read that 1GBx2 are included with the MacPro. For a total of 10GB, which of the following configurations leads to the best performance?

Option1. A1=A2=B1=B2= 2GB, A3=B3=1 GB
Option2. A1=B1=4, A2=B2 = 1 GB
Option3. Open to suggestions.

In terms of performance, is it better to buy larger modules and use as few slots as possible? For a total of 12GB, what is the best configuration? Are there any rule of thumb?