Hi,
Just to follow up on Bret's answer, there is no real scientific reason why the default moved to 4KB pages so you needn't worry that Sybase is saying that is the 'correct' page size, it's entirely down to each persons individual system. Don't forget you have 8KB and 16KB page sizes also that should be considered. For example all SAP applications running on ASE use 16KB page size.
Cheers,
Simon