Opteron system memory scaling (Stream results)

Yesterday went to Fry's and bought a pair of DDR 3200 ECC Registered sticks of RAM 1024 MB each. 1 GB I had before in my Opteron rig felt very yesterday :) So, now I have # GB, but I was wondering about performance effects of having 2 vs 4 memory slots populated. Some documentation (on Crucial's website) made me feel for a moment that having 4 sticks has the effect of memory speeds dropping to 2700 (DDR 333). But at least that is not the case. Re-reading that piece, this only happens when using 2GBs modules in all 4 slots. I do still remember articles on Anandtech and tomshardware (without being able to link to those), and other overclocker's forums, about varying effects of having 4 sticks of RAM vs 2.

The situation is quite common, I should think. You buy a machine with a pair of RAM modules initially, and when you decide to expand, simply doubling initial RAM amount seems somewhat strange. So you end up buying twice the original amount, but how will it work with all 4 memory slots filled, and with memory being of different origin? Anyways, it appeared quite hard to find a benchmark to run to see what my case ends up being... Started with Stream, and here are the results, in MB/s:

	Copy	Scale	Add	Triad
1GB Win32	2012	2037	1899	1891
2GB Win32	2313	2345	2287	2185
3GB Win32	2377	2398	2322	2206
1GB Win64	3773	3699	3226	3039
2GB Win64	4064	4038	3415	3215
3GB Win64	4070	4049	3401	3204

To recap, these tests were produced on Sun Java Workstation W1100z with Opteron 150, using combinations of 2x512 MB and 2x1024 MB RAM modules. 2x512 are original modules shipped, based on Infineon chips. The 2x2048 are Patriot modules with Hynix chips. Good suggestions to run benchmarks that are easy to acquire are welcome. Hopefully those benches should not require extensive setup...