Choosing the right RAID 5 chunk size and filesystem

Hi,

I currently have a freebsd fileserver with just one disk containing
mostly large media files, software mirrors and backups.

Wanting some experience now with linux raid and LVM I'm building a
new system to replace this machine.

I know that RAID 5 chunk size can make a big difference and should
be tuned based on needs, so I was wondering if anyone has any tips
on what I could do to calculate the best chunk size based on my
existing filesystem?

Also, under what circumstances would you recommend using reiserfs
over ext3?  Are there any parameters to mke2fs/mkreiserfs that
should also be tuned based on the existing filesystem?

Thanks,
Andy