I've got 2 memory reviews here with the first from OCAddiction with a review of GeIL's top of the line performance PC3500 Memory.

Also, one of the largest barriers I have encountered wasn't maxing out my processor speed, it was not being able to run my memory faster. Typically there have been two reasons for this: one, the memory simply wouldn't run any faster; or two, the motherboard couldn't push the memory higher. To solve the first problem, GeIL has released 256 megabyte and 512 megabyte sticks of PC3500 RAM. PC3500 RAM is rated to run on a 216.666 megahertz memory bus or 433 megahertz DDR. That's over 100 megahertz higher than any JEDEC certified RAM!

More information at OCAddiction

 

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3dXtreme follows up with their Corsair 256meg XMS3200 DDR Memory review.

Overall if you are looking to upgrade or if you are looking to purchase memory now I would definitly suggest spending a bit more and purchasing pc3200 like Corsair's XMS3200. Not only will it be usable on the kt400 motherboard but the heatspreaders keep it running cool and you should be able to overclock a bit further making pc3200 a very good investement choice.

More information at 3dXtreme