Inherited tables vs non-inherited tables

I've been trying an inherited-table schema for my database and seem to
be getting a performance hit. The old table looked like this:

CREATE TABLE center_out (
subject text,
arm char,
target int4,
rep int4,
success int2, -- end of primary key
exp_date date,
exp_time time,
inter_target_radius int4,
target_radius int4);

Since the fields subject, arm, target, and rep appeared in just about
every other table as the primary key, I made it an inherited table for
the new schema:

CREATE TABLE center_out (
subject text,
arm char,
target int2,
rep int4,
success int2
);

CREATE UNIQUE INDEX pkcenter_out ON center_out (subject, arm, target,
rep, success);

CREATE TABLE center_out_behavior (
exp_date date,
exp_time time,
inter_target_radius int2,
target_radius int2
) INHERITS (center_out);

However, queries such as "SELECT DISTINCT subject FROM center_out"
seem to take 2-3 times longer in the new schema. Does this make sense?
I was hoping that the inherited information would lead to an
easier-to-follow, smaller, and faster database since there wouldn't be
redundant information across tables.

Thanks.
-Tony

PostgreSQL 7.1.3 on i686-pc-linux-gnu, compiled by GCC 2.96