DDR 2100 vs SDRAM

I have a shuttlr ak32L mb. It takes either regular sdram, DDR 1600 and DDR 2100. I am currently running 640 meg of SDRAM. I,ve seen in the forums that everyone loves 2700 DDR and up. How much of an increase will I get going to 2100 DDR (that is the highest my mb will support) and ids it worth the money. Also does anyone know how much difference ther is between the cheaper ram (Kingston valueram or PNY) vs the more expensive (Crucial, Micron) . Also do you thing this upgrade will allow me to overclock further? APPRECIATE ANY HELP YOU CAN GIVE ME

SHULLTE AK32L MOTHERBOARD
WINDOWS XP PRO
VISIONTEK GEFORCE 4 MX 440
LITE-ON BURNER
ATHLON XP 2000 (CLOCKED TO 1900 MXZ)
THERMALTAKE HEATSINK VOLCANO FAN RUNNING AT 100 DEG f

First of all, everyone loves the 2700 and up, is because the ram can reach those FSB speeds during overclocking...

And just looking at your system alone -> GET DDR!! NOW!!

You will benefit! Technically (going by easy numbers) SDR runs at 133FSB, whereas the DDR, utilising the double data rate, kind of runs at 266FSB... SO there is a performance jump, but you may not actually notice for some things! But DDR is a very significant thing, as us SETI crunchers love it, An XP whatever is much faster at crunching in the same system using DDR Ram than an SDR ram system...

And about your motherboard supporting the 2700 ram etc, as you have overclocked, if you are overclocking the FSB, then your computer will support the higher speeds, therefore you could buy the 2700 or up. If you have had to unlock to overclock, then 2100 is the best choice, as to what manufacturer to buy from, I cant really say much, apart from my lovely 256MB Samsung DDR ram which goes to 170FSB...

It depends on your budget and what you do with your computer, If you upgrade, I would say you get about an average of 20% performance increase. PC2700 will get you more but you have to upgrade the motherboard and unlock the Athlon first. Right now DDR price is at its peak, so I don't think you should throw away 640M SDRAM. Wait till next year when nforce2 boards, Barton and pc2700 prices stablize.