reading large BYTEA type is slower than expected

We have recently ported our application to the postgres database. For
the most part performance has not been an issue; however there is one
situation that is a problem and that is the initial read of rows
containing BYTEA values that have an average size of 2 kilobytes or
greater. For BYTEA values postgres requires as much 3 seconds to read
the values from disk into its buffer cache. After the initial read into
buffer cache, performance is comparable to other commercial DBMS that we
have ported to. As would be expected the commercial DBMS are also slower
to display data that is not already in the buffer cache, but the
magnitude of difference for postgres for this type of data read from
disk as opposed to read from buffer cache is much greater.

We have vacuumed the table and played around with the database
initialization parameters in the postgresql.conf. Neither helped with
this problem.

Does anyone have any tips on improving the read from disk performance of
BYTEA data that is typically 2KB or larger?

Mark