If you dont OC, the DDR2 533 will let you run 1:1 with the upcomming Coe 2 Duo/Extreme.
On A64 Am2 platform, you get almost no performance hit while running on memory Divider so faster ram could be usefull especially on X2 while doing a lot of multitasking.
I personally in favor of lower speed better timmings, to get a really clear picture on how Core react to higher bandwith VS lower timmings, I gues we'll have to wait for the release and more torough review.