Table Inheritance / VARCHAR search question

Hi,

I'm hoping someone on this list can save me some unnecessary
benchmarking today

I have the  following table in my system

    BIGSERIAL , INT , INT,  VARCHAR(32)

There are currently 1M records , it will grow to be much much
bigger.  It's used as a search/dispatch table,  and gets the most
traffic on my entire app.

I'm working on some new functionality, which will require the same 3
colums as above but with 3 new VARCHAR(32) columns
    BIGSERIAL , INT , INT,  +VARCHAR(32) , +VARCHAR(32) , +VARCHAR(32)

ie, the new  function shares the same  serial and the  the 2 INT columns

I'm trying to get this to work efficiently on speed and on disk space.

i've figured that my options are:

a)     one table with everything in it
    pro:
        simple
    possible con:
        when i had  something similar in mysql 4 years ago, i had to make
all the varchars chars , because speed was awful.  under this system,
80% of the 3 new VARCHAR fields will always be null, so that  disk
waste will be noticable.  thats only IF there is a speed issue with
VARCHAR searching.

b) keep current table, create new table that inherits and has the 3
new fields
    pro: simple
    possible con:
        i can't find any documentation on how an inherit works behind the
scenes.  is the data cloned into the new table?  is there a join on
every search?  if this is constantly doing a join behind the  scenes,
thats probably not going to work for me

c) move to a 3 table structure
    table1- serial
    table2 - current table, bigserial is not bigint
    table3- bigint + 3 varchars

    pro:
        obviously will work
    con:
        a lot of restructuring

i was going to have both table share a seqeunce, but then i
remembered that the  id is foreign keyed by other tables

if anyone can offer a suggestion, i'd be greatly appreciative