database tuning

hi i need to know all the database overhead sizes and block header sizes etc
etc as I have a very complex database to build and it needs to be speed
tuned beyond reckoning

I have gathered some relevant information form the documentation such as all
the data type sizes and the RM block information but I don't have any
information on INDEX blocks or other general overheads

http://www.peg.com/techpapers/monographs/space/space.html

http://www.postgresql.org/docs/8.1/static/datatype.html

I am using postgres 8.1 if anyone can post links to pages containing over
head information and index block header information it would be most
appreciated as I cannot seem to find anything

Regards

Kelvan