Memory : Slower but in sync with FSB or faster?

[BurningInferno]

Hi all
I have a Gigabyte GA-7VAXP Ultra with the KT400 (not the 'A') and I'm planning to upgrade my cpu to Atholn 3000XP (FSB 333). The KT400 doesn't support FSB400 and that's why I can't upgrade to 3200XP.
The point is that this chipset has only limited support on DDR400. I checked Kingston's website and to my surprise, my motherboard can have up to 512MB DDR400. I currently have 512MB DDR333 and my question is the following : Should I upgrade to DDR400 with only 512MB or is it better to stay in sync with FSB and add another 512MB to reach 1024MB of DDR333?

About CAS latency... my current DDR333 runs at CL2,5 (default). Is this the standard for DDR333 (like the CL3 for DDR400) ?? If I buy a 512MB DDR400 with CL3 as an upgrade and use it as DDR333 will the CL drop to 2.5??

 

[Algere]

I know with my old AXP 2400+ paired with ram running @ DDR400 it was scoring lower on Sandra's memory benchmark than when I had it in-sync with the FSB @ 266.

It was also running on a KT400 board too.

 

[oldman420]

running in sync is better and you will get a much better performance boost by going to a mobile cpu you could get 2 gigs out of a 2400 mobile http://www.centrix-intl.com/?source=froogle&directbuy=yes&itempartnumber=AXMS18 if you can reach fsb 190 x 12.5 thats better tan an xp3200 for sure

 

[Nucro]

Like oldman said running in sync is better so no need to upgrade your ram to PC3200. In fact I think if

Most of the PC3200 rams will work at 166 fsb @Cas 2.5 easy, in fact if you can give more voltage to ram it should do cas 2 at 166fsb.

 

[BurningInferno]

Well, I tested it with my Athlon XP 2000 (FSB 266). I forced the RAM to run at DDR266 and run Sandra (it also run by default at CL2).
Going from DDR266 to DDR333 I only have a 4.46% faster memory with a 25% faster memory bus...
So if you do the calculations, going from 333 to 400 is a 20% increase in bus speed but only a 3.56% in memory!!
I can save 40E and buy a DDR333 without an actual performance loss!

I have also tested the timings of my DDR333.
I reached a 2-2-2-6 without voltage increase and good stability but it actually gave me less that 2% with Sandra (1.92%).
The interesting part here is this : In the BIOS' secret menu (CTRL-F1 at main BIOS screen) there is an option "Fast Command" taking values of "Normal", "Fast" and "Ultra".
With the default timings of the RAM, "Fast" is 5.4% faster than "Normal" and "Ultra" adds another 1.32% !!! I also set 2-2-2-6 and "Ultra" and I got a 9.2% faster than default settings!!! ...always with Sandra...
Can anyone explain me that? What is "Fast Command"? Because it actually boosts RAM more than twiking the timings.

PS: ...set to "Ultra" from now on...