Inheritence versus delete from

Trying to determine the best overall approach for the following
scenario:

Each month our primary table accumulates some 30 million rows (which
could very well hit 60+ million rows per month by year's end). Basically
there will end up being a lot of historical data with little value
beyond archival.

The question arises then as the best approach of which I have enumerated
three:

1) Just allow the records to accumulate and maintain constant vacuuming,
etc allowing for the fact that most queries will only be from a recent
subset of data and should be mostly cached.

2) Each month:
SELECT * INTO 3monthsago_dynamically_named_table FROM bigtable WHERE
targetdate < $3monthsago;
DELETE FROM bigtable where targetdate < $3monthsago;
VACUUM ANALYZE bigtable;
pg_dump 3monthsago_dynamically_named_table for archiving;

3) Each month:
CREATE newmonth_dynamically_named_table (like mastertable) INHERITS
(mastertable);
modify the copy.sql script to copy newmonth_dynamically_named_table;
pg_dump 3monthsago_dynamically_named_table for archiving;
drop table 3monthsago_dynamically_named_table;

Any takes on which approach makes most sense from a performance and/or
maintenance point of view and are there other options I may have missed?

Sven Willenberger