Underclocking DDR400 to allow 3 sticks

Question

From what I understand, the MSI K8T Neo-FIS2R doesn't support 3 sticks of DDR400 RAM.  I'm currently running 2 sticks at DDR400 speeds, and it's fine, but I have an additional stick that I originally purchased with the motherboard, and I want to bring into play (taking my total memory to 1.5GB).
For this to work, I'm assuming that I have to underclock the DDR400 memory to run as DDR333.  I've read that the BIOS should do this automatically, but when I leave the settings to auto (even with only two sticks), the setting shows DDR200, so I think I'll need to use manual settings.
My memory is Samsung K4H560838E-TCCC.  According to their docs, the CL-tRCD-tRP timings 3-3-3, and I was bumping the tRCD up to 4 (according to the AMD recommendations, due to the fast internal memory controller of the AMD64).  The max burst is 8.  I had the final BIOS clock setting (can't recall the name right now) at "Auto", because I could not find a comparable setting in the Samsung docs.  (If you can tell me what that should be, I would appreciate it.)  All seems to work fine with 2 sticks = 1MB.
If I up this to 3 sticks = 1.5GB, I'm afraid that the automatic BIOS settings will still come out to DDR200, which means that I have to underclock this manually.  If so, what settings should I use?  Is it sufficient to change only the DDR400 setting to DDR333, and leave everything else the same?  Or should I use the timing settings from the Samsung docs, as if I were running true DDR333?  The settings vary, however, depending on the exact model number, so I'm not sure which ones I would pick.
I can't afford to be running with an unstable machine, so I can't just try a bunch of settings, dreading a system lock with each one.  At the same time, though, I don't want to be overly conservative in my estimates, and rob myself of needed processing speed.
Then again, perhaps I should be considering whether the machine will be faster with 1GB of DDR400 or 1.5GB or DDR333.  I want to use more for a ram disk, etc., which will have some impact on speed.  The extra memory will make setting this up simpler.  Then again, I'm not usually running so many programs that I would "run out" of memory with 1GB.  Even when I use Photoshop Elements, I can open a couple dozen pictures before it starts to bog down.
I appreciate any guidance that you can give me.
-=> Mike Hanson

Answer 1

unless you encounter stability problems.
The bios should read the spd information on the memory and set the correct settings for you memory.  Now unfortunately this doesn't work for everyone, hence the manual settings option.  
More aggressive settings can give slightly better performance in benchmarks but probably no real world gains and could sacrifice some degree of stability.
If with auto settings you experience stability problems then you would wanto go with less aggresive settings (higher numbers)  for instance I run auto (2,3,2,6)  with out problems.  But if I did have stability problems then it is recomended that I run at (2,4,2,6)
Explanation of (x,x,x,x) in order as listed:
CAS # Latency = 2 clocks
RAS # to CAS # Delay = 3 clocks
RAS # Precharge = 2 clocks
Cycle Time (Tras) = 6 clocks
The lower the settings the more aggressive, the higher, the more conservative (more stable).
One more thing, I would not overclock if stability is #1 on your priority list.
However for us hardcore gamers, and speed freaks, it is fun to play with.  I have had stability problems overclocking with this setup and am running stock.