OCAddiction has a review of GeIL's top of the line performance PC3500 Memory. These guys were pretty impressed with it, so if your overclocking your system and need every last ounce of speed then you'll surely want to take a look at this stuff. Here's a snip:
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!
Read more
here.