Blocks read for index scans

While working on determining a good stripe size for a database, I
realized it would be handy to know what the average request size is.
Getting this info is a simple matter of joining pg_stat_all_tables
and pg_statio_all_tables and doing some math, but there's one issue
I've found; it appears that there's no information on how many heap
blocks were read in by an index scan. Is there any way to get that info?
--
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461