I'm setting up a raid of 4 x 70GB SCSI disks, as a raid 5 array. Setup gives a choice of stripe size.

Can anyone tell me what are the advantages/disadvantages of using larger or smaller stripe sizes?

I'll be using Windows XP.

It mainly depend on what are the main type and size of files you plan to store on them.

They're going to be partitioned. The OS is going to be on one partition and data on another. No huge files, just lots of small to medium ones.
What difference would stripe size make?