Unless u r overclocking, its not worth investing in high-end RAMs. I would suggest u overclock ur present memory to the extent it would go to. If u r lucky, ur present memory may as well run stable (with a little increment of about .1V to its voltage) at 200FSB, but may be at lower timings.
Also, u could wait when DDR500 becomes common, so that the prices of DDR400, DDR433 et al would come down pretty much.
<font color=blue>Just be </font color=blue><font color=red><b>ABU</b></font color=red> - <b><font color=red>A</b></font color=red><font color=blue>lways</font color=blue> <b><font color=red>B</b></font color=red><font color=blue>e</font color=blue> <b><font color=red>U</b></font color=red><font color=blue>seful<b>!</b></font color=blue>