I say that, because I once had PC2-4200 installed and now run PC2-5300 though my datasheet says that only PC2-4200 is supported.
It also says that only 2GB are supported, but have a look at my profile!
It's the same thing for other models. Many users in the german amilo-forum upgraded their RAM in a way that should just not be possible, according to the datasheet. I know no one who complained that an upgrade didn't work due to a change from PC2-4200 to PC2-5300.
The datasheets provided by FSC are not correct in terms of RAM.