Th is something that I haven't done much under Perl, but have done more under C. I think the theory may still be valid in that you want to grab enough of a chunk to make the number of disk accesses lower. If you grab too much, you may start swapping. Also grabbing powers of 2 were more kind due to crossing chunk boundries. (ie grabbing 1050 was about as fast as 2000 in some cases.) But that depends on disk layouts as well.